02 Peacock Mat Peds RSV 508

Implementation and Uptake of Nirsevimab and
Maternal Vaccine for Infant Protection from RSV
Immunization Services Division
Centers for Disease Control and Prevention
June 25, 2025National Center for Immunization and Respiratory Diseases

•National Immunization Survey (NIS):
-Random -digit -dial cellular telephone survey of adults age ≥18 years in the U.S. (all
50 states, 5 local jurisdictions, and territories); all responses are self reported.
-Sample size: ~15,000 adult respondents weekly, ~60,000 adult respondents monthly
-Data are weighted to represent the non- institutionalized U.S. population
•Immunization Information Systems (IISs):
-Confidential, population- based databases that record all vaccine doses administered
by participating providers in a specific geographic area
-ISD receives monthly aggregate data for COVID, influenza, and RSV, and quarterly
line-level, de -identified data for individual immunizations
•Vaccine Safety Datalink:
-Estimates of vaccination coverage are based on electronic health data from multiple integrated health systemsData sources used to estimate U.S. immunization
coverage
Coverage for Nirsevimab and Maternal
Vaccination
Number of infants <8 months old who received nirsevimab+, by month of receipt,
IIS data from 36 U.S. jurisdictions, October 2023– December 2024*
050000100000150000200000250000300000350000
Oct-23 Nov-23 Dec-23 Jan-24 Feb-24 Mar-24 Apr-24 May-24 Jun-24 Jul-24 Aug-24 Sep-24 Oct-24 Nov-24 Dec-24No. of infants
Month of nirsevimab receipt
+Includes infants <8 months of age who received ≥1 dose of nirsevimab prior to January 1, 2025.
*Preliminary IIS data through 12/31/24 from 36 U.S. jurisdictions (AK, AR, AZ, CA, CT, DC, DE, FL, IL, IA, KY, LA, MD, ME, MI,  MN, MO, MS, MT, NJ, NM, NV, NY, OH, OK, PA, SD, TN, TX, VT, WA, WI, WV, WY, NYC, Philadelphia).
0 10000 20000 30000 40000 50000 60000Apr-23
May-23
Jun-23
Jul-23
Aug-23
Sep-23
Oct-23
Nov-23
Dec-23
Jan-24
Feb-24
Mar-24
No. infants who received nirsevimabInfant birth monthInfant age at nirsevimab receipt, by birth month
Apr2023─Mar2024*
0-3 days
4-6 days
7d-<1mo
>=1moAge at
nirsevimab
receipt
*Preliminary IIS data through 12/31/24 from 36 U.S. jurisdictions (AK, AR, AZ, CA, CT, DC, DE, FL, IL, IA, KY, LA, MD, ME, MI,  MN, MO, MS, MT, NJ, NM, NV, NY, OH, OK, PA, SD, TN, TX, VT, WA, WI, WV, WY, NYC, Philadelphia).
0 20000 40000 60000 80000 100000Apr-24
May-24
Jun-24
Jul-24
Aug-24
Sep-24
Oct-24
Nov-24
Dec-24
No. infants who received nirsevimabInfant birth monthInfant age at nirsevimab receipt, by birth month
Apr2024─Dec2024*
0-3 days
4-6 days
7d-<1mo
>=1moAge at
nirsevimab
receipt
*Preliminary IIS data through 12/31/24 from 36 U.S. jurisdictions (AK, AR, AZ, CA, CT, DC, DE, FL, IL, IA, KY, LA, MD, ME, MI,  MN, MO, MS, MT, NJ, NM, NV, NY, OH, OK, PA, SD, TN, TX, VT, WA, WI, WV, WY, NYC, Philadelphia).
Percent of pregnant women ages 18 –49 years vaccinated with RSV vaccine
overall and by race and ethnicity, Vaccine Safety Datalink, 2024 –25
•38.5% of pregnant women were vaccinated overall
•Vaccination coverage ranged from 25.7% among Black, Non -Hispanic (Black)
pregnant women to 52.6% among Asian, Non -Hispanic (Asian) pregnant
women
Data source: Respiratory Syncytial Virus (RSV) Vaccination Coverage, Pregnant Women, United States | RSVVaxView  | CDC
0.26.7 6.914.0 14.7 12.329.938.046.146.750.4
44.7
020406080100
Oct-24 (n=268) Nov-24 (n=401) Dec-24 (n=344) Jan-25 (n=336) Feb-25 (n=368) Mar-25 (n=653)PercentProtection against RSV with maternal vaccination or nirsevimab among infants <8
months* during the RSV season (born since April 2024), National Immunization Survey -
Fall Respiratory Virus Module
Data source: https://www.cdc.gov/rsvvaxview/dashboard/nirsevimab -coverage -infants.html  57% of infants born
April 2024- March 2025
were protected from RSV by maternal vaccination or receipt
of nirsevimab.
*Born April 2024- March 2025

Birthing Hospital Enrollment in VFC to
Facilitate Nirsevimab  Administration
•For infants born during October through March, nirsevimab should be
administered in the first week of life – ideally during the birth
hospitalization.1
•Children who lack commercial insurance coverage (~45%)2 are less likely to
be seen by their primary care provider (PCP) within one week of birth than
are children who are commercially insured.
•Birthing facilities and their staff are critical to ensuring newborns are protected against RSV before hospital discharge, including newborns who qualify for the Vaccines for Children (VFC) program.Protecting Newborns against RSV
1. Use of Nirsevimab for the Prevention of Respiratory Syncytial Virus Disease Among Infants and Young Children: Recommendations  of the Advisory Committee on Immunization Practices
— United States, 2023 | MMWR
2. CDC National Center for Health Statistics: Health Insurance Coverage: Early Release of Estimates From the National Health Interview Survey, January –June 2024
•Participation in the VFC Program:
-Promotes equitable access to all ACIP -recommended vaccines
-Enables newborns to receive the immunizations they need before hospital
discharge
-Reduces hospital’s up -front costs
•Hospitals do not pay for nirsevimab or hepatitis B vaccines for VFC -eligible
children
-Helps provide quality care to all infants who are at risk for RSV infection, regardless of insurance statusBenefits for Birthing Hospitals
•2023
-292 of 2,827 (10%) birthing hospitals were
enrolled in VFC
•Updated policy approaches, new partnerships,
and communication
•2025*ⴕ:
-1,012 (36%) birthing hospitals are enrolled in VFC
-Substantial increase over a two -year period
between October 2023 and March 2025Birthing Hospital Enrollment in VFC
*Data as of March 31,  2025
ⴕ  Data reported by the Provider Education Assessment and Reporting (PEAR) system
•Supply
-Anticipated to be sufficient to meet demand and to be available earlier than
during the 2024 -2025 season
-Earlier supply (1) enables broad availability prior to the start of immunization, (2) promotes confidence in supply and program implementation.
•Planning
-CDC will facilitate equitable availability of RSV monoclonal antibody across jurisdictions
-Pre-season technical assistance around ordering will be provided to jurisdictions
•Increased availability of 50mg doses of nirsevimab  at the beginning of the season
is anticipated.
•Newly licensed clesrovimab can be available once it has been added to CDC's VFC
contracts.Supply and Ordering for RSV Monoclonal Antibody in
the VFC program:  2025- 2026 Season
•In 2024-2025, more infants who were born during RSV season and
received nirsevimab did so in the first month of life compared to those
born in the prior season of administration (2023-2024).
•Maternal immunization and RSV monoclonal antibody protected 57% of
infants born April 2024-March 2025, showing the benefit of offering both
options.
•Increased birthing hospital enrollment and improved early supply of RSV monoclonal antibody should provide greater access to protection from
RSV in this upcoming season. Summary
For more information, contact CDC/ATSDR
1-800- CDC- INFO (232- 4636)
TTY:  1 -888- 232- 6348    www.cdc.gov           www.atsdr.cdc.gov
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry.
Thank you

Summary: Implementation and Uptake of Nirsevimab and  Maternal Vaccine for Infant Protection from RSV Immunization Services Division Centers for Disease Control and Prevention June 25, 2025National Center for Immunization and Respiratory Diseases  •National Immunization Survey (NIS): -Random -digit -dial cellular telephone survey of adults age ≥18 years in the U.S. (all  50 states, 5 local jurisdictions, and territories); all responses are self reported. -Sample size: ~15,000 adult respondents weekly,…


03 MacNeil Mat Peds RSV 508

Effectiveness and impact of RSV
prevention products in infants during
the 2024 –2025 RSV season
Coronavirus and Other Respiratory Viruses Division
June 25, 2025National Center for Immunization and Respiratory Diseases

Product Effectiveness (PE)
•Summary of CDC systems used toevaluate PE
•Effectiveness of nirsevimab and maternal RSV
vaccine during the 2024 –2025 RSV season in
the U.S.
RSV Hospitalization Rates and Product Impact
•Summary of CDC systems used for monitoring
RSV hospitalization rates
•Impact of nirsevimab and maternal RSV
vaccine during the 2024 –2025 RSV season in
the U.S.Agenda
2
Product effectiveness
methods and CDC
systems used for
evaluation
3
Observational VE studies Methods1
Virtual SARS -CoV-2, Influenza,
and Other respiratory viruses
Network (VISION) Test-negative
design2,3,4
New Vaccine Surveillance
Network (NVSN)
Overcoming Network
(Overcoming)Matched Case -
Control5Study designs for observational PE studies
References for study design methods with relevant examples
1Roper L, et. al. A framework for monitoring RSV prevention product effectiveness in the United States.  Vaccine  2025;45:126633
2 Chua H, et. al. The Use of Test -negative Controls to Monitor Vaccine Effectiveness: A Systematic Review of Methodology. Epidemiology  2020;31:43 –64.
3 Moline HL, et al. Respiratory Syncytial Virus Disease Burden and Nirsevimab  Effectiveness in Young Children From 2023 -2024..  JAMA Pediatr  2025;179:179 -187.
4 Payne AB, et. al. Respiratory syncytial virus (RSV) vaccine effectiveness against RSV -associated hospitalisations  and emergency department encounters among adults aged 60 years and older in the USA, October,  2023, to March,  2024: a test -
negative design analysis.  Lancet  2024;404:1547 -1559.
5 Zambrano LD, et. al. Durability of Original Monovalent mRNA Vaccine Effectiveness Against COVID -19 Omicron -Associated Hospitaliz ation in Children and Adolescents - United States, 2021 -2023.  MMWR  2024;73:330 -338Effectiveness = 1 – (odds ratio) x 100%    Odds ratio = 𝑂𝑑𝑑𝑠  𝑜𝑓 𝑖𝑚𝑚𝑢𝑛𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑐𝑎𝑠𝑒𝑠
𝑂𝑑𝑑𝑠  𝑜𝑓 𝑖𝑚𝑚𝑢𝑛𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑐𝑜𝑛𝑡𝑟𝑜𝑙𝑠
4Persons who seek care for
RSV-like illness during
RSV seasonCases
Test positive for
RSVImmunized
Unimmunized
Controls
Test negative for
RSVImmunized
Unimmunized
CDC networks used to assess RSV product effectiveness
in infants and children
VISION
Multi -site network of electronic
health records (EHRs)
160 emergency department (ED)
and 131 hospitals in 6 states
Children visiting a participating ED
or hospital with RSV -like illness are
eligible for inclusionNVSN

Active surveillance for acute
respiratory illness (ARI) in children
7 academic pediatric health
systems in 7 states
Children hospitalized or visiting the
ED for ARI are eligible for
enrollmentOvercoming
Active surveillance for pediatric RSV
with case -control design
26 pediatric intensive care units
(ICUs) in 23 states
Children in a participating ICU with
ARI are eligible for inclusion.
5VISION: https://www.cdc.gov/flu -vaccines -work/php/vaccine -effectiveness/vision -network.html ; NVSN: https://www.cdc.gov/nvsn/php/about/index.html ; Overcoming: https://www.palisi.org/overcomecovid
;
Summary of CDC networks used to assess RSV product
effectiveness in children
VISION NVSN Overcoming
Infant and maternal
immunization dataElectronic health records, state
and city registries, and claims
data (subset of sites)Electronic health records, state
registries, out -of-network
provider records, parent reportElectronic health records,
state registries, provider
records, parent report
Analytic study period October 2024 –March 2025 October 2024 –March 2025 December 2024 –April 2025
Cases RSV-like illness (RLI) with
clinical positive RSV antigen or
nucleic acid amplification test
(NAAT)Acute respiratory illness (ARI)
with RSV detected on
systematic NAAT testingARI with clinical positive
RSV antigen or NAAT
Controls RSV-like illness with negative
RSV NAATAcute respiratory illness (ARI)
with no RSV detected on
systematic NAAT testingARI with negative NAAT;
Case -matched on site, age,
and date of hospitalization
6
Summary of VISION, NVSN, and Overcoming analytic
methods used to assess product effectiveness in children
VISION NVSN Overcoming
Nirsevimab
analytic populationInfants <8 months as of October 1, 2024, or born after October 1, 2024  with no maternal RSV
vaccination receipt
Maternal vaccine
analytic populationInfants born on or after
September 14, 2024  who did not
receive nirsevimabInfants <6 months of age during
the study period who did not
receive nirsevimabNot assessed
Analysis Multivariable logistic regression
models, adjusting for site, age in
months, calendar date, race and
ethnicity, and sex.
Models adjusting for underlying
medical conditions did not
meaningfully change estimates.Multivariable logistic regression
models, adjusting for site, age in
months, and month of enrollment.
Nirsevimab analysis adjusted for
presence of ≥1 high -risk medical
condition for severe RSV
disease; maternal RSV analysis
adjusted for race/ethnicity and
insurance status.Multivariable logistic
regression models, adjusting
for site, age in months,
timing of enrollment,
presence of ≥1 underlying
medical condition, and social
vulnerability index.
Outcomes assessed Hospitalization, emergency
department (ED) visit, intensive
care unit (ICU) admissionHospitalization, ED visit, ICU
admissionICU admission
7
Nirsevimab
effectiveness
during the
2024–2025
RSV season in
the United States
8
Nirsevimab product effectiveness (PE) against RSV -associated emergency department
(ED) visits  among infants in their first RSV season, VISION & NVSN, 2024 –2025
*VISION analysis included children who received nirsevimab  ≥7 days prior to encounter.
†Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, calendar
date, race and ethnicity, and sex.
‡NVSN analysis included children who received nirsevimab  ≥7 days prior to symptom onset.
§Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, month of
enrollment, and presence of >1 high-risk medical condition for severe RSV disease.
IQR: Interquartile Range | CI: Confidence IntervalNirsevimab was effective against RSV -associated ED visits.SYSTEM
Nirsevimab StatusRSV-positive
encounters
N (Col %)RSV-negative
encounters
N (Col %)Median days
since dose
(IQR)Adjusted
PE (95% CI)
VISION1225 2833
No nirsevimab  doses966 (79) 1799 (64)Not Applicable Reference
Nirsevimab, ≥7 days prior*259 (21) 1034 (36) 68 (37 -102) 63 (56 -69)†
NVSN 107 381
No nirsevimab  doses92 (86) 214 (56)Not Applicable Reference
Nirsevimab, ≥7 days prior‡15 (14) 167 (44) 68 (41 -103) 76 (55 -87)§
0 50 100
Product Effectiveness (%)
9
Nirsevimab product effectiveness (PE) against RSV -associated hospitalization
among infants in their first RSV season, VISION & NVSN, 2024 –2025
SYSTEM
Nirsevimab StatusRSV-positive
encounters
N (Col %)RSV-negative
encounters
N (Col %)Median days
since dose
(IQR)Adjusted
PE (95% CI)
VISION286 318
No nirsevimab  doses233 (81) 174 (55)Not Applicable Reference
Nirsevimab, ≥7 days prior*53 (19) 144 (45) 61 (27 -102) 79 (67 -87)†
NVSN 294 378
No nirsevimab  doses263 (89) 229 (61)Not Applicable Reference
Nirsevimab, ≥7 days prior‡31 (11) 149 (39) 52 (27 -87) 82 (71 -88)§
Nirsevimab was effective against RSV -associated hospitalization.0 20 40 60 80 100
Product Effectiveness (%)
*VISION analysis included children who received nirsevimab  ≥7 days prior to encounter.
†Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, calendar
date, race and ethnicity, and sex.
‡NVSN analysis included children who received nirsevimab  ≥7 days prior to symptom onset.
§Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, month of
enrollment, and presence of >1 high-risk medical condition for severe RSV disease. 10
Nirsevimab product effectiveness (PE) against RSV -associated intensive care unit
(ICU) admission among infants in their first RSV season, VISION, NVSN &
Overcoming, 2024 –2025
SYSTEM
Nirsevimab StatusRSV-positive
encounters
N (Col %)RSV-negative
encounters
N (Col %)Median days
since dose
(IQR)Adjusted
PE (95% CI)
VISION 56 318
No nirsevimab  doses 48 (86) 174 (55) Not Applicable Reference
Nirsevimab, ≥7 days prior*8 (14) 144 (45) 56 (25 -97) 82 (57 -93)†
NVSN 73 71
No nirsevimab  doses 67 (92) 40 (56) Not Applicable Reference
Nirsevimab, ≥7 days prior‡6 (8) 31 (44) 52 (24 -84) 88 (63 -96)§
Overcoming 409 263
No nirsevimab  doses 354 (87) 146 (56) Not Applicable Reference
Nirsevimab, ≥7 days prior* 55 (13) 117 (44) 50 (32 -86) 80 (73 -85)¶
Nirsevimab  was effective against RSV -associated ICU admission.0 20 40 60 80 100
Product Effectiveness (%)
*Analysis included children who received nirsevimab  ≥7 days prior to encounter.
†Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, calendar
date, race and ethnicity, and sex.  RSV -negative encounters were those among children hospitalized for RSV -like illness and not limited to children admitted to the ICU.
‡NVSN analysis included children who received nirsevimab  ≥7 days prior to symptom onset.
§Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, month of
enrollment, and presence of  >1 high-risk medical condition for severe RSV disease.
¶Product effectiveness (PE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for age in months, timing of
admission, census region, presence of ≥1 underlying medical condition, and social vulnerability index. Hospital site included  as a repeated measure. The analysis was not limited to matched pairs. 11
Maternal vaccine effectiveness during
the 2024–2025 RSV season in the
United States12
Maternal vaccine effectiveness (VE) against RSV -associated emergency
department (ED) visits  among infants in their first RSV season, VISION, 2024 –2025
SYSTEM
Nirsevimab StatusRSV-
positive
encounters
N (Col %)RSV-negative
encounters
N (Col %)Median days
since birth (IQR)Median days
since dose
(IQR)Adjusted
VE (95% CI)
VISION333 660
No maternal
vaccine262 (79) 428 (65) Not Applicable Not Applicable Reference
Maternal vaccine* 71 (21) 232 (35) 53 (31 -90) 85 (65 -110) 54 (35 -67)†
Maternal RSV vaccine was effective against
RSV-associated ED visits in infants.0 20 40 60 80 100
Vaccine Effectiveness (%)
*VISION analysis included children who were born ≥14 days after maternal RSV vaccine dose.
†Vaccine effectiveness (VE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, calendar
date, race and ethnicity, and sex.
IQR: Interquartile Range | CI: Confidence Interval 13
SYSTEM
Vaccination StatusRSV-positive
encounters
N (Col %)RSV-negative
encounters
N (Col %)Median days since
birth (IQR)Median days
since dose
(IQR)Adjusted
VE (95% CI)
VISION 134 122
No maternal vaccine 109 (81) 77 (63) Not Applicable Not Applicable Reference
Maternal vaccine* 25 (19) 45 (37) 35 (17 -69) 73 (52 -111) 79 (55 -90)†
NVSN 108 213
No maternal vaccine 89 (82) 142 (67) Not Applicable Not Applicable Reference
Maternal vaccine‡19 (18) 71 (33) 32 (17 -58) 71 (50 -103) 70 (28 -88)§Maternal vaccine effectiveness (VE) against RSV -associated hospitalization
among infants in their first RSV season, VISION & NVSN, 2024 –2025
Maternal RSV vaccine was effective against RSV -associated hospitalization in infants.
*VISION analysis included children who were born ≥14 days after maternal RSV vaccine dose.
†Vaccine effectiveness (VE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, calendar date, race and ethnicity, and sex.
‡NVSN analysis included children who born  ≥14 days after maternal RSV vaccine dose
§Vaccine effectiveness (VE) calculated as (1 -adjusted odds ratio)*100, with adjusted odds ratio estimated using multivariable log istic regression model, adjusting for site, age in months, month of enrollment, race/ethnicity, and health
insurance status . 140 20 40 60 80 100
Vaccine Effectivness (%)
•These surveillance systems have different enrollment methodologies and source populations and may
not be directly comparable.
•Residual confounding was possible
•Misclassification of RSV immunization status was possible, although all systems used multiple sources to
verify immunization status
•VISION:
-Cases may have sought care for something other than RSV
-All RSV testing was clinician -directed
-EHR data may not fully capture all underlying medical conditions, which may be associated with likelihood of
immunization and risk of severe RSV disease
•NVSN:
-May not be nationally representative
-Cases may have sought care for something other than RSV
•Overcoming Network:
-Enrollment began after the RSV season started
-All RSV testing was clinician -directed Limitations of product effectiveness analyses
15
Conclusions
16
Summary of RSV prevention product effectiveness (PE) among infants in
their first RSV season, 2024 –2025
Outcome Product CDC Network Product Efficacy* /Effectiveness (95% CI)
RSV-associated ED visitNirsevimabVISION 63 (56 -69)
NVSN 76 (55 -87)
Clinical Trial Not Applicable
Maternal VaccineVISION 54 (35 -67)
Clinical Trial Not Applicable
RSV-associated hospitalizationNirsevimab*VISION 79 (67 -87)
NVSN 82 (71 -88)
Clinical Trial 81 (62 -90)
Maternal Vaccine†VISION 79 (55 -90)
NVSN 70 (28 -88)
Clinical Trial 57 (15 -80)
RSV-associated Intensive Care
Unit (ICU) admissionNirsevimab*VISION 82 (57 -93)
NVSN 88 (63 -96)
Overcoming 80 (73 -85)
Clinical Trial 90 (16 -99)
*Jones et al. MMWR  2023. Available:  https://www.cdc.gov/mmwr/volumes/72/wr/mm7234a4.htm
†Kampmann et al. NEJM 2023. Available: https://www.nejm.org/doi/full/10.1056/NEJMoa2216480 170 20 40 60 80 100
Vaccine Effectivness (%)
•Nirsevimab was effective against RSV -associated
emergency department (ED) encounters,
hospitalization, and critical illness among infants
in their first RSV season during the 2024 –2025
RSV season in the United States.
•Maternal vaccination was effective against RSV -
associated ED encounters and hospitalization
during the 2024 –2025 RSV season in the United
States.
•Ongoing monitoring of post -licensure nirsevimab
and maternal RSV vaccine effectiveness will be
necessary to assess additional outcomes.Product Effectiveness Conclusions
18
Impact of RSV prevention products on U.S.
pediatric RSV -associated hospitalizations
Analyzed data from two active, population -based U.S. surveillance systems
that monitor laboratory -confirmed RSV -associated hospitalizations
RSV-NET NVSN
RESP -NET: Respiratory Virus Hospitalization
Surveillance Network
•RSV-NET, FluSurv -NET, COVID -NET
•Patients of any age from >300 hospitals, 161
counties in 13 states
•https://www.cdc.gov/rsv/php/surveillance/rsv -net.htmlNVSN: New Vaccine Surveillance Network
•Children <18 years old hospitalized with acute
respiratory illness at 7 academic pediatric health
systems in 7 states
•https://www.cdc.gov/nvsn/php/about/index.html
20
Methods
•Ecological analysis that compared RSV -associated hospitalizations and rates between
RSV seasons before and after RSV prevention product introduction
‒Pre-pandemic, before product introduction
▪RSV-NET: 2018 –19, 2019 –20
▪NVSN: 2017 –19, 2018 –19, 2019 –20
‒After product introduction
▪2024 –25, 2nd year of product availability
•Excluded RSV seasons
‒2020 –21, 2021 –22, and 2022 –23 seasons impacted by COVID -19 pandemic
‒2023 –24, 1st year of product availability
▪Low product availability and uptake21
Methods
•Compared adjusted RSV -associated hospitalization and ICU admission rates *
before and after RSV prevention product introduction
–Weekly  (RSV -NET) and monthly  (NVSN) hospitalization rates during 2024 –25
versus same periods in prior seasons
–Cumulative  2024 –25 hospitalization rates compared to pooled rates from prior
seasons
▪Hospitalization rates (RSV -NET and NVSN)
▪ICU admission rates (RSV -NET)
–Estimated rate ratios (RR) comparing cumulative rates
–Estimated relative rate reductions (RRR): (1 -RR) x 100
*RSV -NET rates adjusted for undertesting and test sensitivity; NVSN rates adjusted for enrollment rates, weeks with <7 surveillance days, test sensitivity, and hospital market share
22
•Assessed changes in rates before and after RSV prevention
product introduction for three age groups with different RSV
prevention optionsMethods
23
•Assessed changes in rates before and after RSV prevention
product introduction for three age groups with different RSV
prevention options
‒Infants aged 0 –7 months
▪Eligible for nirsevimab
▪Potentially protected by maternal RSV vaccinationMethods
24

•Assessed changes in rates before and after RSV prevention
product introduction for three age groups with different RSV
prevention options
‒Infants aged 0 –7 months
▪Eligible for nirsevimab
▪Potentially protected by maternal RSV vaccine
‒Children aged 8 –19 months
▪Small number may have been eligible for
nirsevimab based on risk conditionsMethods
25
•Assessed changes in rates before and after RSV prevention
product introduction for three age groups with different RSV
prevention options
‒Infants aged 0 –7 months
▪Eligible for nirsevimab
▪Potentially protected by maternal RSV vaccine
‒Children aged 8 –19 months
▪Small number may have been eligible for
nirsevimab based on risk conditions
‒Children aged 20 –59 months
▪Age group ineligible for RSV prevention productsMethods
26
•Assessed changes in rates before and after RSV prevention
product introduction for three age groups with different RSV
prevention options
‒Infants aged 0 –7 months
▪Eligible for nirsevimab
▪Potentially protected by maternal RSV vaccine
‒Children aged 8 –19 months
▪Small number may have been eligible for
nirsevimab based on risk conditions
‒Children aged 20 –59 months
▪Age group ineligible for RSV prevention productsMethods
Comparison populations
mostly ineligible for RSV
prevention products.
Included  to detect
hospitalization rate
changes unrelated to
RSV product uptake.
27
https://www.cdc.gov/rsvvaxview/dashboard/nirsevimab -coverage -infants.htmlDuring 2024 –25, RSV prevention products were available before RSV season
onset in most states,  with product coverage that increased over time.
•21% to 48% coverage among infants aged
0–7 months across 36 reporting
jurisdictions as of March 2025
•39% of eligible* pregnant women aged
18–49 years received RSV vaccine as of
January 2025Nirsevimab Maternal RSV Vaccine
*includes pregnant women who reached at least 32 weeks’ gestation as of September 1, 2024
https://www.cdc.gov/rsvvaxview/dashboard/pregnant -women -coverage.htmlIIS Nirsevimab Coverage (%)
for 2024–25 Season
28
2018–19
Rate2019–20
Rate2024–25
RateInfants
vs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vsToddlers ChildrenFor an ecological analysis, RSV -associated hospitalization rates can be assessed in three age
groups across different RSV seasons
29

In the absence of new RSV prevention products, RSV -associated hospitalization rates would be
expected to vary by age group, but remain consistent within each age group across seasons.
2018–19
Rate2019–20
Rate2024–25
RateInfants
vs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vsToddlers Children
30

Because new RSV prevention products are only recommended for some children, RSV -associated hospitalization rates
from seasons before product introduction can be compared to 2024 –25 (after product introduction), by age group
2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vsInfants aged 0 –7 months, eligible
for nirsevimab or potentially
protected by maternal RSV vaccineChildren aged 8 –19 months, some of
whom may have been eligible for nirsevimab
based on risk conditionsChildren aged 20 –59 months, age
group ineligible for RSV prevention
products
31

The analysis can assess whether RSV -associated hospitalization rates in 2024 –25 compared to prior
seasons changed more for infants aged 0 –7 months than for children aged 8 –19 and 20 –59 months
2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vs2018–19
Rate2019–20
Rate2024–25
Ratevs vsInfants aged 0 –7 months, eligible
for nirsevimab or potentially
protected by maternal RSV vaccineChildren aged 8 –19 months, some of
whom may have been eligible for nirsevimab
based on risk conditionsChildren aged 20 –59 months, age
group ineligible for RSV prevention
products
32

Results
Combined, RSV -NET and NVSN identified >20,000 children
aged <5 years with RSV -associated hospitalizations
RSV-NET NVSN
2018–20 2024–25 2017–20 2024–25 Total*
Hospitalizations 9,717 7,003 3,119 1,001 20,840
Intensive Care Unit (ICU)
Admissions2,332 251 671 200 3,454
34*Children at two surveillance sites for NVSN and RSV -NET could be documented in both systems. In 2018 –20, 252 hospitalized child ren were enrolled in both systems, with 54 also having an ICU
admission. During 2024 –25, 76 children were enrolled in both systems with 25 having an ICU admission.
Proportions of children aged <5 years with an RSV -associated
hospitalization who were aged  0–7 months decreased, and median age
increased, in 2024 –25 compared to seasons before product introduction
28
1431
1523
1525
22
0102030405060708090100
2018–20 2024–25 2017–20 2024–25Proportion of all children aged <5 years with RSV -associated
hospitalizationChildren aged 20 –59 months
Children aged 8 –19 months
Infants aged 3 –7 months
Infants aged 0 –2 months
Median age in months 7.7 15.4 6.3 12.7RSV-NET NVSN
29%38%51%46%
35
Cumulative adjusted RSV -associated hospitalization rates in 2024 –25
were compared to seasons before product introduction by age group
17.016.0
5.85.3
1.71.1
02468101214161820
RSV-NET NVSN RSV-NET NVSN RSV-NET NVSN
0–7 months 8–19 months 20–59 monthsHospitalization rate per 1,000 children2018-20
(RSV-NET) or
2017-20
(NVSN)
Patton & Moline et al, MMWR 2025; Curns  et al. Pediatrics 202436Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) ea ch season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV underdetection because of
testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction testing compared to serology,
and each site’s estimated market share of acute respiratory illness hospitalizations by age. Error bars denote 95% confidence  intervals (95% CI).
Cumulative adjusted RSV -associated hospitalization rates in 2024 –25
were compared to seasons before product introduction by age group
17.016.0
5.85.3
1.71.110.511.0
8.1
6.3
2.9
1.9
02468101214161820
RSV-NET NVSN RSV-NET NVSN RSV-NET NVSN
0–7 months 8–19 months 20–59 monthsHospitalization rate per 1,000 children2018-20
(RSV-NET) or
2017-20
(NVSN)
2024-25
37
Patton & Moline et al, MMWR 2025; Curns  et al. Pediatrics 2024Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) ea ch season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV underdetection because of
testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction testing compared to serology,
and each site’s estimated market share of acute respiratory illness hospitalizations by age. Error bars denote 95% confidence  intervals (95% CI).
RRR=relative rate reduction, 95%CI = 95% confidence interval
Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) each season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV underdetection  because of
testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction testing compared to serology,
and each site’s estimated market share of acute respiratory illness hospitalizations by age. Error bars denote 95% confidence  intervals.Among infants aged 0–7 months  (eligible for p rotection by nirsevimab or
maternal vaccine ) RSV -associated hospitalization rates were reduced by 38% and
31%  in 2024–25 compared to seasons before product introduction
17.016.0
5.85.3
1.71.110.511.0
8.1
6.3
2.9
1.9
02468101214161820
RSV-NET NVSN RSV-NET NVSN RSV-NET NVSN
0–7 months 8–19 months 20–59 monthsHospitalization rate per 1,000 children2018-20
(RSV-NET) or
2017-20
(NVSN)
2024-25RRR=31%
(95% CI 22 -44)RRR=38%
(95% CI 35 -41)
No reductions
38
Patton & Moline et al, MMWR 2025; Curns  et al. Pediatrics 2024
Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) each season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV
underdetection  because of testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase
chain reaction testing compared to serology, and each site’s estimated market share of acute respiratory illness hospitalizat ions by age. Error bars denote 95% confidence intervals.Cumulative adjusted RSV -associated hospitalization rates in 2024 –25
were compared to prior seasons among subgroups of infants aged 0 –2
and 3–7 months
24.923.4
12.211.5
051015202530
RSV-NET NVSN RSV-NET NVSN
0–2 months 3–7 monthsHospitalization rate per 1,000 children2018-20
(RSV-NET) or
2017-20
(NVSN)
Patton & Moline et al, MMWR 2025; Curns  et al. Pediatrics 202439
RRR=relative rate reduction, 95%CI = 95% confidence interval
Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) each season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV
underdetection  because of testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase
chain reaction testing compared to serology, and each site’s estimated market share of acute respiratory illness hospitalizat ions by age. Error bars denote 95% confidence intervals.RSV-associated hospitalization rates were reduced by 47% in RSV -NET
and 46% in NVSN among infants aged 0 –2 months in 2024 –25
compared to seasons before product introduction
24.923.4
12.211.513.212.6
8.910.1
051015202530
RSV-NET NVSN RSV-NET NVSN
0–2 months 3–7 monthsHospitalization rate per 1,000 children2018-20
(RSV-NET) or
2017-20
(NVSN)
2024-25RRR= 47% (95% CI 43 -50) RRR= 46% (95% CI 35 -57)
RRR= 27% (95% CI 22 -32)RRR=20% (95% CI -4-37)
Patton & Moline et al, MMWR 2025; Curns  et al. Pediatrics 202440
Conclusions
RSV Prevention Product Impact Conclusions
•Two U.S. population -based surveillance
networks demonstrated reductions in RSV -
associated hospitalization rates during 2024 –25
among infants eligible for RSV prevention
product protection
-38% (RSV -NET) and 31% (NVSN) reductions in
2024 –25 compared to RSV seasons before product
introduction among infants aged 0 –7 months
42

Conclusions
•Reductions in RSV -associated hospitalization were
greatest among infants aged 0 –2 months born just
before or during the RSV season
-47% (RSV -NET) and 46% (NVSN) reductions in 2024 –25
-Group at highest risk of hospitalization
-Underscores importance of protection through maternal
vaccination during pregnancy or nirsevimab in first week
of life
•Ongoing monitoring of RSV disease trends —including
severity and age distribution —is critical to assess
sustained impact of RSV prevention products
43
Acknowledgements
▪CDC National Center for Immunizations and Respiratory
Diseases (NCIRD)
▪CDC -funded partners
•VISION
•New Vaccine Surveillance Network (NVSN)
•Overcoming Network
•RSV-NET
44
www.cdc.govFor more information, contact CDC
1-800 -CDC -INFO (232 -4636)
TTY:  1 -888 -232-6348    www.cdc.gov
The findings and conclusions in this report are those of the authors and do not necessarily represent the official
position of the Centers for Disease Control and Prevention.
Photographs and images included in this presentation are licensed solely for CDC/NCIRD online and presentation
use. No rights are implied or extended for use in printing or any use by other CDC CIOs or any external audiences.

Bar labels indicate the incidence rate per 1,000 children.  Rates were calculated using county -specific denominators from the 20 20 US bridged -race population estimates, and population -based numerators based on the observed number of hospitalizations at eac h site adjusted to
account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction testing compared to serology, and each site’s estimated market shar e of ARI hospitalizations by age.
Error bars denote 95% confidence intervals determined based on 1000 bootstrap samples for each rate.RSV-associated hospitalization rates among children <5 years of
age, by season, New Vaccine Surveillance Network, 2017 -2025
Curns et al. Pediatrics 2024; Patton & Moline et al, MMWR 2025.
25.67
13.35
8.41
4.07
1.104.1919.1
12.0
5.3
2.9
0.73.027.0
15.7
8.0
4.4
1.24.423.9
13.7
7.2
3.8
1.03.926.6
16.2
8.7
5.2
1.65.012.0
10.7
6.3
5.8
1.43.7
05101520253035
0-2 Months 3-5 months 6-11 months 12-23 months 24-59 months 0-59 monthsHospitalization rate per 1,000 children
Age Group2017-2018
2018-2019
2019-2020
2017-2020 Average
2023-2024
2024-2025
46
Bar labels indicate the incidence rate per 1,000 children.  Rates were calculated using county -specific denominators from the 20 20 US bridged -race population estimates, and population -based numerators based on the observed number of hospitalizations at eac h site adjusted to
account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction testing compared to serology, and each site’s estimated market shar e of ARI hospitalizations by age.
Error bars denote 95% confidence intervals determined based on 1000 bootstrap samples for each rate.RSV-associated hospitalization rates among children <5 years of
age, by season, RSV -NET, 2018 –2025
RSV-NET unpublished data
22.1
14.8
8.9
6.5
5.0
1.726.8
15.6
10.3
7.9
5.2
1.9
0.41 0.32 0.14 0.16 0.09 0.0427.0
13.7
9.1
6.6
5.2
1.935.7
24.6
18.4
12.3
10.0
4.222.9
16.8
13.6
10.4
7.3
2.613.2
9.8
8.5 8.77.8
2.9
0510152025303540
0-2 months 3-5 months 6-7 months 8-11 months 12-19 months 20-59 monthsHospitalization rate per 1,000 children2018-19 2019-20 2020-21 2021-22 2022-23 2023-24 2024-25
47
RSV-NET NVSNWeekly (RSV -NET) and monthly* (NVSN) adjusted RSV -associated hospitalization rates in 2024 –25 were lower  compared to
prior seasons among infants aged 0–7 months  and
were the same or higher  than prior seasons among children aged 20–59 months
00.20.40.60.811.21.41.61.8
40 42 44 46 48 50 52 2 4 6 8 10 12 14 16 18Adjusted RSV hospitalization rate per 1,000 population
Surveillance week2024-25 Pooled 2018 –2020
Minimum 2018 –2020 Maximum 2018 –2020
00.20.40.60.811.21.41.61.8
40 42 44 46 48 50 52 2 4 6 8 10 12 14 16 18Adjusted RSV hospitalization rate per 1,000 population
Surveillance week2024-25 Pooled 2018 –2020
Minimum 2018 –2020 Maximum 2018 –2020
00.20.40.60.811.21.41.61.8
40 42 44 46 48 50 52 2 4 6 8 10 12 14 16 18Adjusted RSV hospitalization rate per 1,000 population
Surveillance week2024-25 Pooled 2018 –2020
Minimum 2018 –2020 Maximum 2018 –2020Infants aged 0 –7 months
Eligible for protection by nirsevimab or
maternal vaccineChildren aged 8 –19 months
Small number eligible for nirsevimabChildren aged 20 –59 months
Ineligible for either product
0123456
October† November December January February March† April†Monthly RSV -associated hospitalization rate per 1,000 population
Month of RSV Season2024 –25 Pooled 2017 –2020
Minimum 2017 –2020 Maximum 2017 –2020
0123456
October November December January February March† AprilMonthly RSV -associated hospitalization rate per 1,000 population
Month of RSV Season2024 –25 Pooled 2017 –2020
Minimum 2017 –2020 Maximum 2017 –2020
0123456
October November December January February March† April†Monthly RSV -associated hospitalization rate per 1,000 population
Month of RSV Season2024 –25 Pooled 2017 –2020
Minimum 2017 –2020 Maximum 2017 –2020
48
Patton & Moline et al, MMWR 2025*2024 -25 NVSN rates through March 31, 2025. †NVSN rates should be interpreted with caution as relative standard error ≥30 or n <5: 0 –7 months March 2024 -25, 8 –19 months Mar ch 2017 –20 max, 20 –59 months October, March and April 2017 –20 min and April 2017 –20 pooled
RSV-NET rates are adjusted to account for RSV underdetection  because of testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase chain reaction
testing compared to serology, and each site’s estimated market share of acute respiratory illness hospitalizations by age.
RRR=relative rate reduction, 95%CI = 95% confidence interval
Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) each season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV
underdetection  because of testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase
chain reaction testing compared to serology, and each site’s estimated market share of acute respiratory illness hospitalizat ions by age. Error bars denote 95% confidence intervals.RSV-associated ICU admission rates in RSV -NET were reduced by 38%
among infants aged 0–7 months ; no reductions occurred among
children aged 8 –19 and 20 –59 months
5.2
1.4
0.43.2
1.3
0.4
0123456
0–7 months 8–19 months 20–59 monthsICU admission rate per 1,000 children2018-20
2024-25RRR= 38% (95% CI 32 -43)
No reductions
RSV-NET unpublished data49
8.2
3.44.8
2.3
012345678910
0–2 months 3–7 monthsICU admission rate per 1,000 children2018-20
2024-25RRR= 42% (95% CI 34 -48)RSV-associated ICU admission rates in RSV -NET were reduced by 42%
among infants aged 0 –2 months and by 31% among infants aged 3 –7
months
RRR=31% (95% CI 21 -40)
50
RSV-NET unpublished dataRRR=relative rate reduction, 95%CI = 95% confidence interval
Bar labels indicate cumulative laboratory -confirmed RSV -associated hospitalizations per 1,000 children as of April 30 (RSV -NET) or March 31 (NVSN) ea ch season. Rates use U.S. population denominators. RSV -NET rates are adjusted to account for RSV
underdetection  because of testing practices and test sensitivity. NVSN rates are adjusted to account for weeks with <7 days of surveillance, the proportion of eligible children not enrolled, sensitivity of respiratory syncytial virus reverse -transcription polymerase
chain reaction testing compared to serology, and each site’s estimated market share of acute respiratory illness hospitalizat ions by age. Error bars denote 95% confidence intervals.
Meta -analysis of nirsevimab  effectiveness against
RSV-associated hospitalization, 2023 -2024 season
PE (95% CI)
79 (72 -85)
77 (65 -86)
76 (65 -83)
85 (72 -92)
66 (62 -70)
99 (76 -100)
71 (39 -86)
90 (86 -93)
81 (63 -90)
85 (23 -97)
90 (84 -93)
71 (58 -81)
80 (76 -83)
93 (84 -97)
95 (89 -98)
86 (66 -95)
83 (77 -88)
Sumsuzzman  DM et al. Real -world effectiveness of nirsevimab  against respiratory syncytial virus disease in infants: a systematic review and meta -analysis. Lancet Child Adolesc  Health  2025
PE: Product Effectiveness; CI: Confidence IntervalVISION 79 (67 -87)
NVSN 82 (71 -88)
51
Meta -analysis of nirsevimab  effectiveness against
RSV-associated ICU admission, 2023 -2024 season
Sumsuzzman  DM et al. Real -world effectiveness of nirsevimab  against respiratory syncytial virus disease in infants: a systematic review and meta -analysis. Lancet Child Adolesc  Health  2025
PE: Product Effectiveness; CI: Confidence Interval
PE (95% CI)
84 (49 -95)
52 (-17-87)
75 (51 -87)
66 (42 -80)
74 (56 -85)
93 (84 -97)
86 (72 -93)
84 (69 -92)
92 (78 -97)
81 (71 -88)
VISION 82 (57 -93)
NVSN 88 (63 -96)
OC 79 (62 -89)
52
•Argentina
-Razzini  et al.1:  VE against RSV-associated hospitalization  was 81% (95% CI 63 –91) among infants
under age 3 months
-Perez Marc et al.2:  VE against RSV-associated hospitalization was 79% (95% CI 62 –88) among
infants under age 3 months
-Gentile et al.3:  VE against RSV-associated hospitalization was 79% (95% CI: 51 –91) among infants
under age 6 months
•UK
-Williams et al.4:  VE against RSV-associated hospitalization was 72% (95% CI: 48 –85) among infants
under age 3 monthsMaternal RSV vaccine effectiveness estimates from
Argentina and UK
1Razzini JL et al. Impact and Effectiveness of Universal Respiratory Syncytial Virus Vaccination During Pregnancy on Infant Ho spitalizations in Buenos Aires: A Retrospective Cohort Study.   VeriXiv .  2025
2Pérez Marc G et al. Real -world effectiveness of RSVpreF  vaccination during pregnancy against RSV -associated lower respiratory tract disease leading to hospitalisation  in infants during the 2024 RSV season in
Argentina (BERNI study): a multicentre , retrospective, test -negative, case –control study.  The Lancet Infectious Diseases.   2025
3Gentile A et al. Maternal Immunization With RSVpreF  Vaccine: Effectiveness in Preventing Respiratory Syncytial Virus –associated Hospitalizations in Infants Under 6 Months in Argen tina: Multicenter Case –control
Study. The Pediatric Infectious Disease Journal .  2025
4Williams TC et al. Bivalent Prefusion F Vaccination in Pregnancy and Respiratory Syncytial Virus Hospitalisation  in Infants: Results of a Prospective, Multi -Centre, Test -Negative Study. Available at SSRN:
https://ssrn.com/abstract=5184994 or http://dx.doi.org/10.2139/ssrn.5184994  53
•Models did not adjust for healthcare utilization behavior or specific
underlying characteristics between vaccinated and unvaccinated patientsProduct Effectiveness Analyses – Controlling for
Confounding
54VISION NVSN Overcoming
Analysis Multivariable logistic regression
models, adjusting for site, age in
months, calendar date, race and
ethnicity, and sex.
Models adjusting for underlying
medical conditions did not
meaningfully change estimates.Multivariable logistic regression
models, adjusting for site, age in
months, and month of enrollment.
Nirsevimab analysis adjusted for
presence of ≥1 high -risk medical
condition for severe RSV
disease; maternal RSV analysis
adjusted for race/ethnicity and
insurance status.Multivariable logistic
regression models, adjusting
for site, age in months,
timing of enrollment,
presence of ≥1 underlying
medical condition, and social
vulnerability index.

Summary: Effectiveness and impact of RSV  prevention products in infants during  the 2024 –2025 RSV season Coronavirus and Other Respiratory Viruses Division June 25, 2025National Center for Immunization and Respiratory Diseases  Product Effectiveness (PE) •Summary of CDC systems used toevaluate PE •Effectiveness of nirsevimab and maternal RSV  vaccine during the 2024 –2025 RSV season in  the U.S. RSV Hospitalization Rates and Product Impact  •Summary of CDC systems used for monitoring  RSV…


04a DeSilva Mat Peds RSV 508

Prenatal RSVpreF  Vaccine Safety
2023 –2024 Respiratory Season
The Vaccine Safety Datalink (VSD)
Malini DeSilva, MD, MPH
Presentation to ACIP
June 25, 2025
© HealthPartners 2Vaccine Safety Datalink (VSD)
•Collaborative project between
CDC and 13 integrated
healthcare organizations
•Monitors safety of vaccines used
in the U.S., primarily through
observational multisite studies
•Includes data on ~15.5 million
individuals across all sites
annually (~4.5% of U.S.
population)
•Annual birth cohort ~ 115,000
•Data is organized using a
common data dictionary with
standardized coding systems

© HealthPartners 3Prenatal RSVpreF  vaccine 2023 –2024 season
•ACIP recommendation 9/22/23:
•32–36 weeks gestation with
seasonal administration
•RSVpreF  clinical trial1
identified non -significant
imbalances among vaccinated
compared to placebo in:
•Preterm births
•Gestational hypertension and
preeclampsia
Photomicrograph of RSV using indi rect immunofluorescent
antibody under fluorescent lighting.
https://wwwn.cdc.gov/phil/Details.aspx?pid=6484
1Simoes EAF, Center KJ, Tita ATN, et al. Prefusion F Protein -Based Respiratory Syncytial Virus Immunization in Pregnancy. N Engl J Med . Apr
28 2022;386(17):1615 -1626. doi:10.1056/NEJMoa2106062
© HealthPartners 4❖Acute outcomes within 42 days of vaccination
❖Preterm birth (birth <37 weeks gestational age)
❖Small for Gestational Age (SGA) at birth
❖Stillbirth (antepartum)
❖Hypertensive disorders of Pregnancy (HDP):
•Gestational hypertension (GHTN) - New onset HTN after 20 weeks
gestation
•Preeclampsia - New onset or worsening chronic HTN after 20 weeks
gestation with or without severe features
•Eclampsia - Convulsive manifestation of HDP with no other etiology
•HELLP Syndrome (hemolysis, elevated liver enzymes, and low
platelets)Prenatal RSVpreF  vaccine safety outcomes
© HealthPartners 5Methods - Target trial emulation design
Protocol
Component
Eligibility criteria Pregnant women 16 –49 years with gestational age 32 –<37 weeks
during 9/22/2023 – 1/31/24 or 2/29/24 for two sites
Treatment
strategies•RSVpreF  vaccination (exposed)
•No RSVpreF  vaccination (unexposed)
Assignment
proceduresExposed women matched 1:1 to unexposed on:
•VSD site
•Propensity to be vaccinated*
•Gestational week
Follow -up period •Index date (vaccination or gestational day of vaccine for
unexposed match) through 2 weeks after pregnancy end
•Follow up censored at crossover to RSVpreF  vaccinationRecreating a randomized experiment from observational data
*Covariates included: Maternal age, calendar week at pregnancy start, # of weeks with prenatal care,
race/ethnicity, comorbidities (i.e., HTN, DM, GHTN, GDM, obesity, substance use), history of preterm labor,
poor fetal growth, supervision of high -risk pregnancy, enrollment, and gestational week
© HealthPartners 6Analysis
•Estimated risk ratios with 95% Confidence Interval (CI) using Log
binomial model with robust variance with adjustment for nulliparity
•For small for gestational age at birth, matched set excluded if infant
weight not available for either infant in matched pair
•For hypertensive disorders of pregnancy, matched set excluded if onset
occurs before or on index date for either woman
© HealthPartners 7Balance plot before and after matching
•SMD =  standardized mean differences for
variables included in the propensity score
before and after matching.
•Common way to assess covariate balance
after matching
•Interpretation: -0.2 to 0.2 = small difference
between groups
Notes:
•*Race/Ethnicity
•LMP = last menstrual period
•Enrollment = continuous health plan enrollment from 90
prior to LMP through index week
•ICD-10 codes for:
•High Risk = O09.* (Supervision of care for a high -
risk pregnancy)
•Poor fetal growth = O36.5
•Preterm labor history = O09.21, Z87.51

© HealthPartners 8Matched cohort* characteristics, N = 13,966
RSVpreF  Vaccinated, n (%) Unvaccinated match, n (%)
Age group
•16–24 years 1405 (10.1) 1595 (11.4)
•25–29 years 3151 (22.6) 3439 (24.6)
•30–34 years 5461 (39.1) 5272 (37.7)
•35–39 years 3286 (23.5) 3020 (21.6)
•40–49 years 663 (4.7) 640 (4.6)
Race/Ethnicity
•Asian 3039 (21.8) 2635 (18.9)
•Black 862 (6.2) 991 (7.1)
•Hispanic 4459 (31.9) 4691 (33.6)
•White 4542 (32.5) 4541 (32.5)
•Other/Unknown 1064 (7.6) 1108 (7.9)
≥1 other vaccine during
pregnancy13758 (98.5) 11315 (81.0)
Nulliparity 5914 (46.4) 4853 (38.7)
*Not unique individuals due to crossover from unvaccinated to vaccinated
© HealthPartners 91–6 and 1 –21 day acute safety outcome risks among pregnant women
receiving RSVpreF vaccine and unvaccinated matches

© HealthPartners 101–42 day acute safety outcome risk among pregnant women
receiving RSVpreF vaccine and unvaccinated matches

© HealthPartners 11Preterm birtha risk among pregnant women receiving RSVpreF
vaccine and unvaccinated matches
Matched
pairs, NRSVpreF vaccinated Unvaccinated matchAdjusted Risk
Ratio (95% CI)b
N events* Preterm birth % N events* Preterm birth %
13,966 563 4.0 627 4.5 0.90 (0.80 –1.00)
aPreterm  birth = birth <37 weeks gestational age
bAdjusted  for nulliparity
*Events only included through date of censoring when unvaccinated pair crosses over to vaccinated
© HealthPartners 12SGAa at birth risk in infants born to RSVpreF  vaccinated
pregnant person or unvaccinated pregnant matches
Matched
pairs, NRSVpreF vaccinated Unvaccinated matchAdjusted Risk
Ratio (95% CI)b
N events* SGA at birth % N events* SGA at birth %
11,822 799 6.8 774 6.5 0.99 (0.90 –1.09)
aSGA  at birth = Small for gestational age at birth; birth weight <10th percentile for gestational age
compared with a U.S. reference population1
bAdjusted  for nulliparity
*Events only included through date of censoring when unvaccinated pair crosses over to vaccinated
 Note: 11,822 matched pairs with complete infant weight data (85%)
Talge NM, Mudd LM, Sikorskii  A, Basso O. United States birth weight reference corrected for implausible gestational age estimates. Pediatrics . May
2014;133(5):844 -53. doi:10.1542/peds.2013 -3285
© HealthPartners 13Stillbirth risk in RSVpreF  vaccinated pregnant women or
unvaccinated pregnant matches
Matched
pairs, NRSVpreF  vaccinated Unvaccinated matchAdjusted Risk
Ratio (95% CI)a
N events*Stillbirths per
1000N events*Stillbirths per
1000
13,966 11 0.79 10 0.72 1.09 (0.46 –2.58)
aAdjusted  for nulliparity
*Events only included through date of censoring when unvaccinated pair crosses over to vaccinated
© HealthPartners 14Hypertensive disorders of pregnancy (HDP) risk among pregnant women
receiving RSVpreF vaccine and unvaccinated matches, N = 13,474
Outcome RSVpreF  vaccinated Unvaccinated matchAdjusted Risk
Ratio (95% CI)a
N events* % N events* %
Any HDP 2344 17.4 2056 15.3 1.09 (1.03 –1.15)
Eclampsia OR
HELLP40 0.3 50 0.4 0.77 (0.51 –1.16)
Preeclampsia 1198 8.9 1021 7.6 1.12 (1.03 –1.21)
Gestational
hypertensionb1069 8.8 939 7.8 1.10 (1.01 -1.19)
aAdjusted  for nulliparity
bMatched  pairs = 12104; excludes matched pairs with chronic hypertension
*Events only included through date of censoring when unvaccinated pair crosses over to vaccinated
© HealthPartners 15Evaluation of rates of cesarean delivery, admissions following birth
hospitalization, and lengths of stay for patients with hypertensive
disorders of pregnancy (HDP) by RSVpreF vaccination status
HDP Severity indicatorRSVpreF
vaccinated
N = 2344Unvaccinated
match
N = 2056
N (%) N (%)
Cesarean delivery 795 (33.9) 675 (32.8)
HDP admission ≤ 14 days following birth
hospitalization184 (7.8) 165 (8.1)
Length of stay >3 days for birth hospitalization
InfantaCesarean delivery 125 (17.8) 123 (21.4)
NSVD 93 (6.8) 70 (5.9)
MotherCesarean delivery 384 (49.0) 310 (46.0)
NSVD 277 (18.3) 245 (17.9)
NSVD = normal spontaneous vaginal delivery
aMissing : RSVpreF  vaccinated = 282 ; Unvaccinated = 300
© HealthPartners 16

© HealthPartners 17
•Retrospective observational cohort study of patients who delivered at 32 0/7
weeks’ gestation or later at 2 NYC hospitals 9/22/23 – 1/31/24
•Stratified analyses by site and insurance status, association remained among
those with private insurance and at 1 of 2 sites

© HealthPartners 18❖RSVpreF  vaccine not associated with increased risk for
•Acute safety outcomes
•Preterm birth
•SGA at birth
•Stillbirth
❖RSVpreF vaccine associated with small but statistically
increased risk for HDP
•Potential residual confounding or outcome misclassification
•Severity of HDP similar between vaccinated and unvaccinated women based on
rates of c -section, admission following birth hospitalization, and length of stay
❖2024 –2025 season analysis pendingConclusions from 2023 –2024 respiratory season findings
© HealthPartners 19HealthPartners
❖Malini DeSilva
❖Elyse Kharbanda
❖Jacob Haapala
❖Gabriela Vazquez -Benitez
❖Leslie Kuckler
❖Jingyi Zhu
❖Sunita Thapa
❖Nicole Trower
❖VSD site PIsOur Team
Weill Cornell Medicine
•Heather Lipkind
Kaiser  Northwest
•Kimberly Vesco
CDC
•Eric Weintraub
•Elizabeth Quincer
© HealthPartners 20•Onset = 1st HDP diagnosis at or after 20+0 weeks GA
•Evaluate as combined outcome (any HDP) and individual outcomes
•For individual outcomes, only include most severe outcome:
Hypertensive disorders of pregnancy diagnoses
Patient GHTN Pre-eclampsia Eclampsia OR HELLP
1 X
2 X X
3 X X X
Count 0 2 1GHTN → preeclampsia → Eclampsia = HELLP
GHTN = gestational hypertension; HELLP = hemolysis, elevated liver enzymes, and low
platelet syndrome; GA = gestational ageHypertensive Disorders of Pregnancy (HDP)
© HealthPartners 21Acute outcomes
Outcome Risk window(s)
(days)Background
rate/10,000*RSVpreF  clinical trial,
N=3682, n (%)**
Anaphylaxis 0–1 n/a n/a
Fever 1–7 3.3 3%
Malaise / fatigue 1–7 11.4 46%
Skin and soft tissue or local allergic reactions 1–7 7.0 41%
Acute disseminated encephalomyelitis 1–21, 1 –42 0 n/a
Acute myocardial infarction 1–21, 1 –42 0.3 n/a
Appendicitis 1–21, 1–42 0.6 n/a
Bell's Palsy 1–21, 1–42 0.8 n/a
Disseminated intravascular coagulation (DIC) 1–21, 1–42 0.3 n/a
Guillain -Barré syndrome 1–21, 1–42 0 n/a
Immune thrombocytopenic purpura (ITP) 1–21, 1–42 7.6 n/a
Lymphadenopathy / lymphadenitis 1–21, 1–42 4.6 <0.1%
*Identified from unvaccinated pregnant persons, COVID -19 medically attended acute outcomes 1 –7 or 1 –21 day evaluation
**RSVPreF  Phase 3 clinical trial electronic diary for 7 days after vaccination
n/a = not available
© HealthPartners 22Acute outcomes, continued
Outcome Risk window (d) Background
rate/10,000*
Myocarditis / pericarditis 1–21, 1–42 0
Pulmonary embolism (PE) 1–21, 1–42 0.1
Seizure 1–21, 1–42 0.8
Stevens -Johnson syndrome or toxic epidermal necrolysis 1–21, 1–42 0/a
Stroke, hemorrhagic 1–21, 1–42 0.4
Stroke, ischemic 1–21, 1–42 0.4
Thrombosis with thrombocytopenia syndrome (TTS) 1–21, 1–42 n/a
Thrombotic thrombocytopenic purpura (TTP) 1–21, 1–42 n/a
Transverse myelitis 1–21, 1–42 n/a
Trigeminal neuralgia and related disorders 1–21, 1–42 0.1
Venous thromboembolism (VTE) 1–21, 1–42 0.4
*Identified from unvaccinated pregnant persons, COVID -19 medically attended acute outcomes 1 –21 day evaluation
© HealthPartners 23Previous VSD studies evaluation HDP
Vaccine IIV Tdap COVID -19 IIV in successive
pregnancies
Time period* 6/1/2022 –7/31/2009 1/1/2010 –11/15/2012 6/1/21 – 1/31/22 1/1/2004 –
12/31/2018
Age of
participants14–49 14–49 16–49 any
GA at exposure any <20 weeks <20 weeks any
HDP outcomes ICD-9 codes:
•GHTN (642.3,
642.9); vax ≥ 20
weeks GA
•Mild preeclampsia
(642.4)
•Severe
preeclampsia or
eclampsia (642.5 -
642.7)ICD-9 codes
occurring ≥20 weeks
GA:
•GHTN (642.3x,
642.9x)a
•Preeclampsia
(642.4x -642.8x )bICD-10 codes ≥20
weeks GA –2 wks
postpartum :
•Gestational HTN
(O13.x)
•Preeclampsia -
eclampsia -HELLP
syndrome ( O14.x,
O15.x, and O16.x)•Preeclampsia
(642.4x, 642.5x,
642.7x; O11.x,
O14.x )
•Eclampsia (642.6x;
O15.x)
*may refer to vaccine administration dates, pregnancy end date, or pregnancy start date
a 642.3x, 642.4x, 642.9x = 2 outpatient or 1 inpatient diagnosis
b 642.5x -642.7x = inpatient diagnosis
© HealthPartners 24Inactivated Influenza Vaccine
Citation: Kharbanda EO, Vazquez -Benitez G, Lipkind H, Naleway A, Lee G, Nordin JD; Vaccine Safety Datalink Team. Inactivated inf luenza vaccine during
pregnancy and risks for adverse obstetric events. Obstet Gynecol. 2013 Sep;122(3):659 -67. doi: 10.1097/AOG.0b013e3182a1118a. PMID: 23921876.
© HealthPartners 25Tdap
Kharbanda EO, Vazquez -Benitez G, Lipkind HS, Klein NP, Cheetham TC, Naleway A, Omer SB, Hambidge SJ, Lee GM, Jackson ML, McCarth y NL,
DeStefano F, Nordin JD. Evaluation of the association of maternal pertussis vaccination with obstetric events and birth outco mes. JAMA. 2014 Nov
12;312(18):1897 -904. doi: 10.1001/jama.2014.14825. PMID: 25387187; PMCID: PMC6599584.
© HealthPartners 26COVID -19
Vesco KK, Denoble AE, Lipkind HS, Kharbanda EO, DeSilva MB, Daley MF, Getahun D, Zerbo O, Naleway AL, Jackson L, Williams JTB , Boyce TG, Fuller CC, Weintraub
ES, Vazquez -Benitez G. Obstetric Complications and Birth Outcomes After Antenatal Coronavirus Disease 2019 (COVID -19) Vaccinatio n. Obstet Gynecol. 2024 Jun
1;143(6):794 -802. doi: 10.1097/AOG.0000000000005583. Epub  2024 Apr 17. PMID: 38626447; PMCID: PMC11090513.
© HealthPartners 27IIV in successive pregnancies
•At least 2
successive,
singleton births
between 1/1/2004 –
12/31/2018
Getahun D, Liu IA, Sy LS, Glanz JM, Zerbo O, Vazquez -Benitez G, Nelson JC, Williams JT, Hambidge SJ,
McLean HQ, Irving SA, Weintraub ES, Qian L. Safety of the Seasonal Influenza Vaccine in 2 Successive
Pregnancies. JAMA Netw  Open. 2024 Sep 3;7(9):e2434857. doi: 10.1001/jamanetworkopen.2024.34857.
PMID: 39298167; PMCID: PMC11413712.

Summary: Prenatal RSVpreF  Vaccine Safety  2023 –2024 Respiratory Season The Vaccine Safety Datalink (VSD) Malini DeSilva, MD, MPH Presentation to ACIP June 25, 2025 © HealthPartners 2Vaccine Safety Datalink (VSD) •Collaborative project between  CDC and 13 integrated  healthcare organizations •Monitors safety of vaccines used  in the U.S., primarily through  observational multisite studies •Includes data on ~15.5 million  individuals across all sites  annually (~4.5% of U.S.  population) •Annual birth…


04b Daley Mat Peds RSV 508

Monitoring the Safety of Nirsevimab
in Infants Birth through <8 Months
June 25, 2025Matthew F. Daley, MDPreliminary Results from the Vaccine
Safety Datalink for the 2024 -2025 Season
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•No conflicts of interest
•Presenting on behalf of the Vaccine Safety Datalink (VSD) teamDisclosures and Acknowledgments
Nirsevimab  Safety Surveillance Slide 2
Background
Slide 3
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Long -acting monoclonal antibody, licensed for prevention of lower
respiratory tract disease in infants caused by RSV
•Recommendations for use:
oAll infants aged birth through <8 months (if no RSV vaccine during pregnancy)
oHigh-risk infants aged 8 -19 months
•High efficacy in phase 3 trial, high effectiveness post -licensure
•Severe shortage during 2023 -2024 season
•RSV prevention ( nirsevimab  or vaccine): 72% uptake in VSDNirsevimab  Overview
Nirsevimab  Safety SurveillanceRef: 1) Muller WJ et al, N Engl J Med 2023;388(16):1533 -1534; 2) Jones JM et al, MMWR 2023;72(34):920 -925.
3) Moline HL et al, JAMA Pediatr  2025;179(2):179 -187. 4) Irving SA et al, Pediatrics 2025;155(6):e2024070240.
Slide 4
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Across 3  randomized trials: n=3,184 received nirsevimab , n=1,284
received placebo, n=304 received palivizumab
•Adverse events generally balanced among infants who received
nirsevimab  versus comparator
•Adverse events of special interest included 7 nirsevimab -exposed
infants with rashes, primarily papular  or maculopapular
•No anaphylaxis, no serious hypersensitivity -type reactions reported
•No immune complex diseases reportedNirsevimab  Safety, Clinical Trials
Nirsevimab  Safety SurveillanceRef: 1) Muller WJ et al, N Engl J Med 2023;388(16):1533 -1534. 2) Mankad VS et al, Pathogens 2024;13(6):503.
Slide 5
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Additional post -licensure safety data needed, including assessment
of rare adverse events, and when nirsevimab  given during routine
care in a general patient population
•Objective: To investigate the safety of nirsevimab , by examining pre -
specified adverse events among nirsevimab  recipients in the Vaccine
Safety Datalink (VSD)
•Nirsevimab  is a passive immunization; CDC and ACIP requested that
VSD evaluate its safetyPost -Licensure Safety of Nirsevimab
Nirsevimab  Safety Surveillance Slide 6
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Collaboration between CDC and 13 healthcare organizations
•Observational; uses electronic health record (EHR) data
•Has ~15.5 million individuals overall; annual birth cohort ~115,000
•Data characteristics:
oElectronic health records, claims, immunization information systems
oDiagnoses, vaccines, medications ordered
oInpatient, emergency departments, outpatient
•VSD applies a range of analytic methods to address confounding,
including self -controlled designsVaccine Safety Datalink (VSD)
Nirsevimab  Safety SurveillanceRef: 1) McNeil MM et al, Vaccine. 2014 Sep 22;32(42):5390 -8.
Slide 7
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
VSD in 2025
Nirsevimab  Safety Surveillance
 Slide 8
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Received nirsevimab , n=36,719
•Adverse events monitored, self -controlled risk interval (SCRI):
oAll analyses stratified by age group (neonates; infants)
oSeizures, ITP, drug reaction, fever or sepsis (neonate cohort only)
oNone showed elevated risk
•Exposure -dependent events: monitored case counts
oAnaphylaxis: no cases detected
oNon-anaphylactic allergic reactions: urticaria, often same day as nirsevimabSafety Results, VSD, 2023 -2024 Season
Nirsevimab  Safety Surveillance Slide 9
Methods
Slide 10
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Setting: all VSD data -contributing sites
•Population: all infants 0 days through <8 months of life who received
nirsevimab  between October 1, 2024, and February 1, 2025
•Same -day vaccines: study included all nirsevimab -exposed infants,
regardless of whether they received vaccines same day as nirsevimab
•Health insurance enrollment: through control window
•Study design: primarily used SCRI
•Excluded infants born to someone who received RSV vaccine during
pregnancyMethods Overview
Nirsevimab  Safety Surveillance Slide 11
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Self-controlled risk interval is a form of self -controlled case series study
•Commonly used design in vaccine safety studies
•Rationale: exposed (to vaccine, or to nirsevimab ) often differ in important
characteristics from unexposed; these characteristics typically not
measured in electronic health record (EHR) data and can confound safety
assessments
•These are within -individual designs; control for measured and unmeasured
confounders that do not vary over time; example, a prevalent chronic
conditionSelf-Controlled Designs in Safety Studies
Nirsevimab  Safety Surveillance Slide 12Ref: 1) Nie X et al, Expert RevVaccines 2022;21(3):313 -324. 2) Weldeselassie  YG et al, Epidemiol Infect 2011;139(12):1805 -
17. 3) Li R et al, J Biopharm Stat 2016;26(4):686 -93. 4) Bots SH et al, Am J Epidemiol. 2025;194(1):208 -219.
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Diagnoses in first month of life often related to pregnancy, delivery,
newborn -specific conditions
•Health care utilization different in first month of life
•Lags in health insurance enrollment
•With the exception of birth dose of hepatitis B vaccine, earliest all
other vaccines recommended: 38 days of age
•Separate safety analyses:
oNewborns: defined as 0 days through 37 days of age
oInfants (out of newborn period): 38 days through <8 months of ageAge Effects
Nirsevimab  Safety Surveillance Slide 13
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Rationale for pre -specified adverse events:
oBiologic plausibility
oClinical trial data
oExpert opinion
oFeedback from ACIP RSV Work Group
•Identified based on ICD -10 diagnosis codes, laboratory data
(platelet counts)Adverse Events Monitored
Nirsevimab  Safety Surveillance Slide 14
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Outcomes for Nirsevimab Safety Surveillance Study
Nirsevimab  Safety SurveillanceAdverse event Design
Seizures Self-controlled risk interval
Immune thrombocytopenia (ITP) Self-controlled risk interval
Drug reaction Self-controlled risk interval
Fever or sepsis (neonates only) Self-controlled risk interval
Anaphylaxis Counts monitored
Non-anaphylactic serious allergic reaction Counts monitored
Autoimmune, immune complex disease Outcomes rare, may have long latency; examine as
case -control at end of surveillance
Slide 15
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Self-Controlled: Risk and Control Windows
Nirsevimab  Safety SurveillanceAdverse eventAge at nirsevimab
administrationRisk
window
(days)Control
window
(days) Setting
Seizure 0-37 days 0-7 8-21 Inpatient, ED
38 days to <8 months 0-7 8-21 Inpatient, ED
Immune thrombocytopenia 0-37 days 1-21 22-42 Inpatient, ED, outpatient
38 days to <8 months 1-21 22-42 Inpatient, ED, outpatient
Drug reaction 0-37 days 0-7 8-15 Inpatient, ED
38 days to <8 months 0-7 8-15 Inpatient, ED
Fever or sepsis (neonates
only)0-37 days 0-7 8-15 Inpatient, ED
Slide 16
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Exposure -Dependent Events: Case Counts Monitored
Nirsevimab  Safety SurveillanceAdverse eventAge at nirsevimab
administrationRisk
window
(days) Setting Manual review
Anaphylaxis 0-37 days 0-2 Inpatient,
EDAll cases will be manually
reviewed
38 days to <8 months 0-2 Inpatient,
EDAll cases will be manually
reviewed
Non-anaphylactic allergic
reactions0-37 days 0-7 Inpatient,
EDCases reviewed if
indicated
38 days to <8 months 0-7 Inpatient,
EDCases reviewed if
indicated
Slide 17
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Outcomes for Nirsevimab  Safety Surveillance Study
Nirsevimab  Safety SurveillanceAdverse event ICD-10 codes Additional information
Seizure G40, R56, P90 First episode in 30 days
Immune
thrombocytopeniaD69.3, D69.6, P61.0 Also required platelets <50,000; first episode in
90 days
Drug reaction P93, T80.22, T80.29,
T80.8, T80.9Example: “Infection following…therapeutic
injection”; first episode in 30 days
Fever or sepsis
(neonates only)P36.9, R50.82, R50.83,
R50.9, T81.1, T81.4First episode in 30 days
Anaphylaxis T80.5, T78.2, T88.6, P81.1 First episode in 30 days
Non-anaphylactic serious
allergic reactionT80.6, T78.3, L50.0,
L50.1, L50.9, P83.88First episode in 30 days
Slide 18
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•For each pre -specified outcome:
oIdentify cases that occur within either risk or control window
oTwo observations per individual: One per control window and risk
window
oInformative cases have outcome in one window but not the other
oCohort must have at least one outcome in each window to estimate
effect
•Models stratified by age group
•Fixed -effects Poisson regression
oIndividual: Within person comparison across windows controls for
measured and unmeasured time -invariant factorsAnalytic Methods: SCRI Analysis
Nirsevimab  Safety Surveillance Slide 19
Results
Slide 20
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Children 0 days old to < 8 months old 01OCT24 -01FEB25
(n=117,427)
Enrolled from at least 38 days old and at least 1 day between 01OCT24 -01FEB25
(n=92,418, 79%)
Nirsevimab
(n=43,532, 47%)
No RSV vaccine during pregnancy
 (n=41,869, 96%)
38 days to < 8 months at index
(n=28,208, 67%)
Administered prior to season
 (n=154, <1%)Administered this season
(n=28,054, 99%)0-37 days old at index
(n=13,661, 33%)
Administered this season
(n=9,855, 81%)Administered prior to season
(n=3,806, 19%)RSV vaccine during pregnancy
(n=1,663, 4%)No nirsevimab
(n=48,886, 53%)
Nirsevimab Safety SurveillanceStudy Flow
Slide 21
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Doses by
Week of Age
Nirsevimab  Safety SurveillanceNote :
0 week=aged 0 -6 days
1 week=aged 7 -13 days
And so forth
Slide 22

KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Neonate
Cohort:
Doses by
Days of Age
Nirsevimab  Safety Surveillance Slide 23

KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Among neonates (0 -37 days old) who received nirsevimab :
oN=2,954 (20%): received on same day as hepatitis B vaccine
•Among infants 38 days through <8 months who received nirsevimab :
oN=24,847 (84%): received on same day as vaccines
oMost common combination: nirsevimab  plus hepatitis B, rotavirus, DTaP, Hib,
pneumococcal, and polio vaccines (n=15,252)Simultaneous (Same -Day) Receipt of Vaccines
Nirsevimab  Safety Surveillance Slide 24
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Self-controlled Risk Interval Results: Seizures
Nirsevimab  Safety SurveillanceAdverse
eventAge
groupn Risk
window
(days)Control
window
(days)N cases
in risk
windowN cases
in
control
windowRR 95% CI P-value
Seizures 0-37
days9,855 0-7 8-21 4 2 3.50 0.64, 19.11 0.148
38 days
to <8
months28,054 0-7 8-21 5 2 4.38 0.85, 22.55 0.078
•2023 -2024 season: non -significant also; no elevated risk of seizures
Slide 25
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Self-controlled Risk Interval Results: ITP
Nirsevimab  Safety SurveillanceAdverse
eventAge
groupn Risk
window
(days)Control
window
(days)N cases
in risk
windowN cases
in
control
windowRR 95% CI P-value
ITP 0-37
days9,817 1-21 22-42 0 0 N/A N/A N/A
38 days
to <8
months28,023 1-21 22-42 1 0 N/A N/A N/A
•Case definition required a diagnosis, and  a platelet count below 50,000, within
21 days of each other, taking first of 2 dates
Slide 26
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Self-controlled Risk Interval Results: Drug Reaction
Nirsevimab  Safety SurveillanceAdverse
eventAge
groupn Risk
window
(days)Control
window
(days)N cases
in risk
windowN cases
in
control
windowRR 95% CI P-value
Drug
reaction0-37
days9,855 0-7 8-15 0 0 N/A N/A N/A
38 days
to <8
months28,054 0-7 8-15 0 0 N/A N/A N/A
Slide 27
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Self-controlled Risk Interval Results: Sepsis and Fever
Nirsevimab  Safety SurveillanceAdverse
eventAge
groupn Risk
window
(days)Control
window
(days)N cases
in risk
windowN cases
in
control
windowRR 95% CI P-value
Sepsis
and fever0-37
days9,855 0-7 8-15 4 9 0.44 0.14, 1.44 0.18
•Only for newborn cohort (not conducted for 38 days to <8 months of age)
•Additional exploratory analysis performed to assess whether nirsevimab  could
cause fever, leading to sepsis workup (blood, CSF cultures)
oAn imbalance detected in cultures obtained in risk vs. control windows
oManual review of sample of charts showed no consistent pattern of concern (neonates
typically had reasons other than fever for cultures being done)
Slide 28
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Exposure -Dependent Events: Hypersensitivity Reactions
Nirsevimab  Safety SurveillanceAdverse event Age group n Risk
window
(days)N cases
in risk
windowRate per
10K person
month
Anaphylaxis 0-37 days 9,855 0-2 0 0
38 days to <8
months28,054 0-2 0 0
Other allergic
reaction0-37 days 9,855 0-7 14 54.93
38 days to <8
months28,054 0-7 4 5.46
•Anaphylaxis and other allergic reactions: exposure -induced outcomes; only
assess within potential risk windows
•“Other allergic reaction” cases: n=17 with diagnosis code for urticaria and n= 1
“serum reaction” (also for urticaria); majority on same day as nirsevimab
Slide 29
Summary
Slide 30
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Among a population of >74,000 (across two seasons) neonates and
infants exposed to nirsevimab :
oNo evidence of increased risk of seizures, ITP, drug reaction, fever and sepsis
oNo cases of anaphylaxis
oSmall number of cases of non -anaphylactic allergic reactions in both years,
primarily coded as urticaria
•Provides reassuring data regarding the safety profile of nirsevimab
when used in routine clinical practice
•Additional data extraction needed for late -season nirsevimab  use;
findings preliminarySummary
Nirsevimab  Safety Surveillance Slide 31
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Three planned assessments
oAfter 2023 -2024 respiratory season
oPreliminary assessment 2024 -2025 season (through January, presented today)
oEnd of surveillance assessment (data extraction July 2025)
•Manual record review of any anaphylaxis cases
•Planned case -control study of autoimmune and immune complex
disease; however, appear to have too few cases to study this group of
outcomes at presentSurveillance Continues
Nirsevimab  Safety Surveillance Slide 32
Questions?
Slide 33
KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Doses by
Week, All
Formulations
Nirsevimab  Safety Surveillance Slide 34

KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
Doses by
Week by
Formulation
Nirsevimab  Safety Surveillance Slide 35

KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•SmartVax  (Western Australia):
o4,340 parents texted hyperlink to report adverse events (27.5% responded)
o18 (1.5%) respondents sought medical attention within 3 days of nirsevimab
oSymptoms at presentation included gastrointestinal issues, fatigue, local
reaction, fever, refusal to feed, unsettled behavior
oNo serious adverse events reported
•Maternity department, French hospital
oExposed accepted nirsevimab  (n=477); unexposed declined (n=40)
oSurveyed at 2 hours, days 7, 14, 30
oMore frequent reports of regurgitation in nirsevimab -exposed on day 30Other Nirsevimab  Safety Surveillance
Nirsevimab  Safety SurveillanceRef: 1) Carcione D et al, PIDJ, 2025 (in press). 2) Ocana de Sentuary C et al, eClinicalMedicine  2025;79:102986
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KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH
•Misclassification of exposure: missing nirsevimab  doses
•Misclassification of outcomes
•Safety assessment limited to pre -specified outcomes of interest
•Main analyses were regardless of vaccines received on same day; if
positive safety signal, can be difficult to disentangle effect of vaccines
from effect of nirsevimab
•Although risk and control windows are short, time -varying covariates
could bias results
•In a population size of >74,000, unable to assess risk of very rare
adverse eventsStudy Limitations
Nirsevimab  Safety Surveillance Slide 37

Summary: Monitoring the Safety of Nirsevimab in Infants Birth through <8 Months June 25, 2025Matthew F. Daley, MDPreliminary Results from the Vaccine Safety Datalink for the 2024 -2025 Season KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH •No conflicts of interest •Presenting on behalf of the Vaccine Safety Datalink (VSD) teamDisclosures and Acknowledgments Nirsevimab  Safety Surveillance Slide 2 Background Slide 3 KAISER PERMANENTE INSTITUTE FOR HEALTH RESEARCH •Long -acting monoclonal antibody,…