May 17, 2025 — Washington, D.C. — A new study reveals a significant decline in respiratory syncytial virus (RSV) hospitalizations among U.S. infants during the 2024–25 season, thanks in part to the introduction of two powerful prevention tools: a maternal RSV vaccine and a monoclonal antibody treatment for infants.
RSV is a leading cause of hospitalization among infants in the United States, especially during the winter season. However, recent data from two national surveillance systems indicate that hospitalization rates for babies up to 7 months old dropped significantly last winter compared to pre-pandemic seasons.
RSV Hospitalization Rates Drop by Over 40%
According to a study published on May 8 in the CDC’s Morbidity and Mortality Weekly Report (MMWR), the RSV hospitalization rate among infants up to 7 months of age fell to 8.5 per 1,000 in the 2024–25 season—down 43% from the 15 per 1,000 rate observed during the 2018–2020 seasons. These earlier seasons are considered the most recent typical RSV seasons unaffected by the COVID-19 pandemic.
Another surveillance system, the New Vaccine Surveillance Network, which monitors pediatric hospitals in seven major U.S. cities, also showed a 28% decline in hospitalization rates among the same age group. The most dramatic drop—up to 52%—was observed in infants under 2 months old.
Role of Maternal Vaccine and Monoclonal Antibody
The 2024–25 season was the first where both RSV preventive products were widely available. The maternal RSV vaccine, recommended by the CDC, is administered during the third trimester (typically from September to January) and transfers protective antibodies to the fetus. This passive immunity protects newborns for around six months after birth.
Meanwhile, nirsevimab, a long-acting monoclonal antibody, is given to babies born during or entering RSV season (October to March). It offers protection for at least five months and is recommended for all infants under 8 months of age.
Both tools work by targeting the RSV fusion (F) protein, preventing the virus from entering and infecting lung cells.
Expert Commentary
Dr. Kawsar Talaat, a vaccine researcher at Johns Hopkins Bloomberg School of Public Health, praised the findings: “To see a decrease in RSV hospitalization rates is really remarkable,” she said. “Infants are particularly vulnerable to RSV because of their small airways and lack of prior immunity. These tools are a game-changer.”
She added, “We’re moving toward a future where RSV hospitalizations among young infants could become rare in the U.S. But it’s also crucial to make these protections available globally, especially in low-resource countries where RSV causes the most harm.”
Looking Ahead
As RSV prevention continues to evolve, the U.S. health community is optimistic about sustained reductions in infant hospitalizations. With continued access to vaccines and antibody treatments, experts believe that RSV-related complications can be significantly minimized in the most vulnerable populations.
References
- Patton, M. E., et al. (2025, May 8). Interim evaluation of respiratory syncytial virus hospitalization rates among infants and young children after introduction of respiratory syncytial virus prevention products — United States, October 2024 – February 2025. Morbidity and Mortality Weekly Report, 74, 273. https://www.cdc.gov/mmwr/volumes/74/wr/mm7416a1.htm?s_cid=mm7416a1_w
- Fleming-Dutra, K. E., et al. (2023, October 13). Use of the Pfizer respiratory syncytial virus vaccine during pregnancy for the prevention of respiratory syncytial virus-associated lower respiratory tract disease in infants: Recommendations of the Advisory Committee on Immunization Practices – United States, 2023. Morbidity and Mortality Weekly Report, 72, 1115. https://www.cdc.gov/mmwr/volumes/72/wr/mm7241e1.htm?s_cid=mm7241e1_w
- Jones, J. M., et al. (2023, August 25). 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. Morbidity and Mortality Weekly Report, 72, 920. https://www.cdc.gov/mmwr/volumes/72/wr/mm7234a4.htm?s_cid=mm7234a4_w