Document text
Work group considerations and
clinical considerations for clesrovimab
Maternal and Pediatric RSV Session
Coronavirus and Other Respiratory Viruses Division
June 25, 2025U.S. Centers for Disease Control and Prevention
•Work group considerations and interpretations of uptake, safety,
effectiveness, and impact studies
•Review of clinical considerations
-Clesrovimab recommendations compared with nirsevimab
-Clesrovimab storage, handling, and administrationOutline
2
•Nirsevimab was effective against RSV -associated emergency
department encounters, hospitalization, and critical illness among infants in
their first RSV season
•Maternal vaccination was effective against RSV -associated ED encounters
and hospitalizations
•An estimated 57% of infants were either born to vaccinated mother
orreceived nirsevimab
•Compared with prior to RSV immunization introduction, RSV -associated
hospitalization rates were reduced by ~30 –40% among eligible infants and
by half among infants aged 0 –2 monthsSummary of RSV immunization effectiveness, uptake,
and impact for the 2024 -25 RSV season
3
•The impact of RSV immunizations to decrease severe RSV disease in infants
during the 2024 –25 RSV season in the RSV -NET and NVSN networks is clear1
•Increasing uptake is important in order to further reduce burden of RSV
disease
-Higher impact has been seen in other countries that have attained higher uptake
of these immunizations2–6
-Important to maximize availability of RSV immunizations, including providing
infant RSV antibody during birth hospitalization
-The increase in birthing hospital enrolled in the Vaccine For Children (VFC)
program is important, but challenges remain
Workgroup considerations on RSV immunization
effectiveness, uptake, and impact
RSV-NET RSV -Associated Hospitalization Surveillance Network; NVSN: New Vaccine Surveillance Network
1Patton 2025 MMWR 2 Bloomfield 2025 Medical Journal of Australia ;3Dessers 2025 Belgian Journal of Paediatrics ; 4García‐García 2025 Influenza and Other Respiratory Viruses ; 5Ares -Gomez 2024
Lancet ID ; 6Mazagatos 2024 Influenza Other Respir Viruses ; 4
•During the reporting period since approval until March 31, 2025, the most
frequently reported adverse events involved patients who developed RSV
infections despite prior receipt of nirsevimab, and included signs,
symptoms, or complications of these infections (e.g., bronchiolitis).
•No product safety labeling updates have been made since serious
hypersensitivity reactions with nirsevimab were added on February 23,
2024.
•No additional safety signals have been identified at this time.
•Errors involving incorrect nirsevimab dose or incorrect product (e.g., adult
vaccine being given to infant) continue to be reported.
•FDA will continue routine pharmacovigilance for nirsevimab. Summary of FAERS1 postmarketing adverse events and
medication errors reporting with nirsevimab
1FDA Adverse Event Reporting System (FAERS) Database | FDA 5
•Study of 37,909 infants that received nirsevimab during 2024 -2025 season
using self -controlled risk interval
•No increased risk observed for seizures, immune thrombocytopenia (ITP),
drug reactions, sepsis, or fever
•No cases of anaphylaxis and 18 (~0.05% of doses) cases of allergic reaction
reported, primarily hivesSummary interpretation of Vaccine Safety Datalink
nirsevimab study
6
•FAERS and VSD safety data are reassuring
•Continued monitoring of safety importantWorkgroup interpretation of nirsevimab safety
FAERS: FDA Adverse Event Reporting System; VSD: Vaccine Safety Datalink; CSF: cerebrospinal fluid 7
•Matched cohort with ~14,000 pairs of vaccinated -unvaccinated pregnant
women
•No increased risk observed for most outcomes, including fever, fatigue,
stroke, seizure, Bell’s palsy, ITP , pulmonary embolism, preterm birth, infant
being born small for gestational age, stillbirth
•Association of maternal RSV vaccine and HDP overall (adjusted odds ratio
[aOR]: 1.09 [95% CI, 1.03 –1.15]) and preeclampsia ( aOR: 1.12 [95% CI,
1.03 –1.21])
-Severity of HDP similar among vaccinated and unvaccinated
-Potential residual confounding (e.g., including parity in the propensity matching)
and outcome misclassification due the difficulty in determining the timing of
when HDP first occurs and lack of chart reviewVaccine Safety Datalink maternal vaccine study
summary
ITP: Immune Thrombocytopenic Purpura; HDP: hypertensive disorders of pregnancy 8
•Overall study findings were reassuring, including lack of association of
preterm birth and vaccination
•WG continues to feel that the benefits of maternal RSV vaccination clearly
outweigh the potential risks
•WG was split on importance of the association of vaccination and HDP
-Some were concerned that an imbalance of HDP was seen in multiple studies
(phase 3 clinical trial, published retrospective cohort study, postmarketing study),
and felt it was important that healthcare providers discuss the potential risk of
HDP with pregnant women
-Some were not concerned about this association since the effect size was small,
and there was no increased severity in vaccinated vs. unvaccinated women with
HDP and no overall association of vaccination with preterm birth; American
College of Obstetricians and Gynecologists was in agreement with this opinionWork group interpretation of maternal vaccine
Vaccine Safety Datalink study findings
9 HDP: hypertensive disorders of pregnancy
•Long -acting, monoclonal antibody manufactured by Merck
•Passive immunization
•Single -dose, manufacturer -filled syringe
-105 mg/0.7 mL
-Same dose for all infants regardless of weightInfant RSV Antibody –Clesrovimab
•Clesrovimab and nirsevimab recommendations would be the same for use
in infants younger than 8 months of age born during or entering their first
RSV season
-No preferential recommendation for use of clesrovimab versus nirsevimab
•Only nirsevimab1 recommended for children ages 8 through 19 months
who are at increased risk of severe RSV disease and entering their second
RSV season
-Infants eligible to receive nirsevimab when entering second RSV season could
have received nirsevimab or clesrovimab for first RSV season
-No effectiveness or safety concerns for using clesrovimab for first RSV season and
nirsevimab for second RSV seasonProposed use of clesrovimab versus nirsevimab
1 Clesrovimab not recommended for this age group because it is not approved by FDA for this indication 11
•One dose for infants younger than 8
months of age born during or
entering their first RSV season
(administration during October through
March in most of the continental U.S.) if:
-The mother did not receive RSV vaccine
during pregnancy
-The mother’s RSV vaccination status is
unknown
-The infant was born less than 14 days after
maternal RSV vaccination
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 12
Proposed recommendations for use
ofRSV antibody immunizations
(nirsevimab or clesrovimab) in infants
< 8 months
•Born to mothers who may not mount an adequate immune response to
vaccination (e.g., immunocompromising conditions)
•Born to mothers who have conditions associated with reduced
transplacental antibody transfer (e.g., living with HIV infection)
•Infants who have procedures leading to loss of maternal antibodies (e.g.,
cardiopulmonary bypass, extracorporeal membrane oxygenation [ECMO],
exchange transfusion)
•Infants with substantially increased risk for severe RSV disease
(e.g., hemodynamically significant congenital heart disease, ICU admission
with oxygen requirement at discharge) When RSV antibody may be considered for
infants born to vaccinated mothers1
RSV Immunization Guidance for Infants and Young Children | RSV | CDC | ICU: intensive care unit; 1 For infants aged <8 months during their first RSV season
Choose one product to prevent severe RSV disease in infants
Most infants will not need both maternal vaccination and an RSV antibody.
Maternal RSV vaccination
- Pfizer AbrysvoInfant RSV antibody
-Nirsevimab
-Clesrovimab- or -
Infant RSV antibody and maternal vaccination have
different administration windows to provide optimal
protection to the infant
Optimal timing for infant RSV administration is shortly before the RSV season
Administration should be targeted shortly before the start of their first RSV season and continued during the
season for those who have not received a dose
Forinfants born shortly before or during the RSV season , immunize within 1 week of birth, ideally during the birth
hospitalization
RSV seasonality differs based on climate
RSV Immunization Guidance for Infants and Young Children | RSV | CDC
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
In jurisdictions with differing RSV seasonality (e.g., Alaska, southern Florida,
Puerto Rico, and other jurisdictions with tropical climates), providers should
follow state, local, or territorial guidance on the timing of administration.
Administer the correct RSV immunization product
Infant RSV
antibody* onlyInfants and Some
Young Children
Abrysvo (Pfizer)
onlyDuring Pregnancy
Older Adults
Do not administer
RSV antibody*, Arexvy ,
or mResvia during
pregnancy.Do not administer
Abrysvo, Arexvy , or
mResvia to infants or
children.Abrysvo (Pfizer )
Arexvy (GSK)
mResvia (Moderna )
Do not administer RSV
antibody* to older adults.
*Includes nirsevimab, clesrovimab, and palivizumab.
Clesrovimab (or nirsevimab) and palivizumab
•If clesrovimab or nirsevimab is
given to an infant or child… …then do not give palivizumab
during the same RSV season.
Use of Nirsevimab for the Prevention of Respiratory Syncytial Virus Disease Among Infants and Young Children: Recommendations of the Advisory C ommittee on Immunization Practices — United
States, 2023 | MMWR , AAP Recommendations for the Prevention of RSV Disease in Infants and Children | Red Book Online | American Academy of Pediatr ics
Clesrovimab*
or nirsevimabPalivizumab
Infant RSV antibody administration
Beyfortus Prescribing Information (fda.gov) Enflonsia Prescribing Information.pdf•Route
-Intramuscular injection
•Site
-Vastus lateralis muscle of anterolateral thigh
-The gluteal muscle should not be used.
•Coadministration
-Simultaneous administration with vaccines is
acceptable.
Clesrovimab storage and handling
Store refrigerated between 2 °C and 8 °C (36°F and 46 °F).
Use within 48 hours of removing from refrigerator.
-May be kept at room temperature, between 20 °C and
25°C (68°F and 77°F), for a maximum of 48 hours
Do not freeze.
Protect from light.Do not shake.
Enflonsia Prescribing Information.pdf
•If RSV antibody is administered alone:
-Report suspected adverse events (AEs) to MedWatch
-www.fda.gov/medwatch
•If RSV antibody is administered simultaneously with any
vaccine:
-Report suspected AEs to Vaccine Adverse Event Reporting System
(VAERS)
-vaers.hhs.gov
-Additional reporting to MedWatch is not necessaryHow to report adverse events after infant RSV
antibody administration
RSV Immunization Guidance for Infants and Young Children | RSV | CDC
For 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.