13/12/2025
Report: RSV immunization 80% effective against infant
ICU admission
November 20, 2025
Melissa Jenco, Senior News Editor
Article type: News
Topics: Infectious Diseases , RSV , Vaccine/Immunization
Respiratory syncytial virus (RSV) immunization nirsevimab is 80% effective against intensive care unit (ICU)
admission, according to a new study.
“These findings add to growing evidence supporting the effectiveness of monoclonal antibody immunization
against severe outcomes from RSV infection in infants during their first RSV season and can be used by
clinicians and parents to guide use of this prevention product,” authors from the Centers for Disease Control
and Prevention (CDC) and Overcoming RSV Network wrote in the Morbidity and Mortality Weekly Report
(MMWR).
RSV is a leading cause of ICU admission for infants. Researchers set out to look at how well nirsevimab can
protect them.
The team used data from patients younger than 1 year admitted to one of 27 pediatric ICUs from Dec. 1,
2024, to April 15, 2025. They compared 457 infants with a positive RSV test to 302 infants with respiratory
symptoms who tested negative for RSV. About 14% of those who tested positive had received nirsevimab
compared to 45% of those who tested negative.
Nirsevimab was 80% effective against RSV-associated ICU admission. Effectiveness was higher at 7-59
days (86%) than at 60-183 days (66%). The immunization also was 83% effective against acute respiratory
failure.
Infants with RSV were in the hospital for a median of six days and in the ICU for a median of four days,
despite most previously being healthy. Length of hospital and ICU stays was similar for those without RSV.
Two patients with RSV and two without required extracorporeal membrane oxygenation. One infant with
RSV and four without died.
While the study has several limitations like the potential for misclassification of infants as being unprotected
from RSV, the results align with previous studies.
Health officials first recommended nirsevimab in August 2023 and since then have approved a maternal
vaccination and a second monoclonal antibody, clesrovimab.
The AAP recommends RSV immunization with nirsevimab or clesrovimab for infants under 8 months of age
born during or entering their first RSV season if their pregnant parent was not vaccinated during that
pregnancy. Infants and children 8 months through 19 months at high risk of severe RSV disease entering
their second RSV season should receive nirsevimab, as clesrovimab is not indicated for children in this age
group.
The ideal time for immunization is in the birthing hospital, but historically many hospitals have not been
enrolled in the Vaccines for Children (VFC) program, which provides free vaccines to children whose
families can’t afford them and to children of American Indian or Alaska Native heritage.
The CDC has been working with professional organizations and health departments to enroll more hospitals
in the VFC program so they can provide RSV immunizations. In another report in the MMWR on Thursday,
researchers found 36% of birthing hospitals were enrolled in the spring of 2025, up from 27% in the fall of
2023.
“Birthing hospital enrollment can support expanded access to RSV immunization among infants at highest
risk for severe disease,” authors wrote.
Resources
AAP policy Recommendations for the Prevention of RSV Disease in Infants and Children
RSV immunization administration visual guide
Information for parents from HealthyChildren.org on RSV
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