Hospitalization rates for respiratory syncytial virus (RSV) fell by half among babies under 3 months this season, the first in which two new immunizations were widely available, a new study showed.
“Thousands of our youngest children are hospitalized with RSV each year, and I’m thrilled to finally have effective ways to protect them,” said Sean T. O’Leary, M.D., M.P.H., FAAP, chair of the AAP Committee on Infectious Diseases. “We have the opportunity to bring hospitalization rates down even further if we increase the number of mothers and babies getting immunized.”
RSV is the leading cause of hospitalization among U.S. infants. The virus causes about 50,000 to 80,000 hospitalizations and 100 to 300 deaths per year in children under 5 years, according to the Centers for Disease Control and Prevention (CDC).
In the fall of 2023, health officials approved two new products to help prevent RSV — a maternal vaccine RSVpreF (Abrysvo from Pfizer) given during pregnancy and monoclonal antibody nirsevimab (Beyfortus from Sanofi and AstraZeneca) given to infants under 8 months as well as some high-risk children ages 8-19 months.
A new study published today in the CDC’s Morbidity and Mortality Weekly Report aimed to look at the impact of these products by comparing hospitalization rates in the 2024-’25 season to those in 2018-’20 using two surveillance networks.
For infants under 3 months, about 22 of every 1,000 children were hospitalized in the earlier years, which fell to about 11 or 12 children per 1,000 (45%-52% reduction).
For children under 8 months, about 15 of every 1,000 children were hospitalized in 2018-’20, which dropped to about 9-11 children per 1,000 (28%-43% reduction). Rates dropped even more if excluding Houston where the RSV season started before products were widely administered.
Declining hospitalizations came despite data suggesting a more severe RSV season in 2024-’25. Rates for older children who mostly were ineligible for immunization were higher than they were in 2018-’20, according to the study.
“The findings suggest the importance of protecting infants born during the RSV season through either maternal vaccination during pregnancy or nirsevimab administration in the first week of life, ideally during the birth hospitalization,” authors wrote.
As of February 2025, about two-thirds of infants under 8 months had protection from one of the two products, according to the study.
Another new immunization product for infants may be on the horizon. Merck’s clesrovimab is a long-acting monoclonal antibody and is proposed for use in infants under 8 months of age born during or entering their first RSV season, similar to nirsevimab. It is awaiting approval from the Food and Drug Administration.
Resources
- AAP RSV resources, including information on nirsevimab ordering, dosing, coding and a visual guide for nirsevimab administration
- AAP Red Book chapter on RSV
- Information for parents from HealthyChildren.org on RSV symptoms and when to call a doctor
- Information from the CDC on using nirsevimab
- Information from the American College of Obstetricians and Gynecologists on maternal RSV vaccine Abrysvo
