Fewer RSV Hospital Admissions Among Infants Given Nirsevimab

CATEGORY: IMMUNE HEALTH

Respiratory syncytial virus infects nearly all children by age two, and it is a leading reason young infants end up in the hospital. In a pooled analysis of 27 real-world studies from five countries, infants who received nirsevimab, a long-acting antibody injection against RSV, had 83% lower odds of being hospitalized for the virus than infants who did not.¹

Borrowed Armor Rather Than a Vaccine

A vaccine trains an infant’s immune system to build its own defenses, which takes time. Nirsevimab skips the training. It supplies ready-made antibodies in a single injection, antibodies being the proteins that latch onto a virus and block it from infecting cells. The difference is closer to lending a newborn armor than to teaching one to forge it. A single dose is designed to cover an infant’s first RSV season, the months when severe illness is most likely, and several countries began offering it to all infants in 2023.

32 Programs Found, 27 With Poolable Data

Researchers searched the medical literature from January 2023 through February 2025 and turned up 32 real-world studies of infant nirsevimab programs in France, Italy, Luxembourg, Spain and the United States. Of those, 27 had data that could be pooled. The studies compared infants in their first year who received nirsevimab in routine care against infants who did not, counting who was admitted to the hospital for RSV, who needed intensive care, and who developed an RSV-related lower respiratory tract infection over the season. That last term covers infections reaching the airways and lungs, such as bronchiolitis or pneumonia.

81% Lower Intensive-Care Odds, and the Same Length of Stay

Immunized infants had 83% lower odds of RSV-related hospitalization, 81% lower odds of an intensive-care admission and 75% lower odds of an RSV-related lung infection. Among infants hospitalized anyway, the stay ran about as long either way. These were observational studies rather than randomized trials, so they establish a link without establishing cause, and families who chose immunization may differ in other ways from families who did not. All the data came from five high-income countries with strong health systems. Protection was substantial rather than total: some immunized infants were still hospitalized.

Randomized trials land in the same place. HARMONIE gave more than 8,000 European infants either nirsevimab or no preventive treatment, and RSV hospitalization came out 83% lower in the treated group, almost exactly the real-world figure.² An earlier trial against a dummy injection found 75% fewer RSV lung infections needing medical care among healthy late-preterm and term infants.³

Key Takeaways

• Infants given nirsevimab had 83% lower odds of RSV hospitalization and 81% lower odds of intensive care than unimmunized infants across 27 real-world studies in five countries, and a randomized trial in over 8,000 infants produced the same 83%.
• The pooled studies were observational, which means a link rather than settled cause; nirsevimab is not a vaccine but a single injection of ready-made antibodies covering an infant’s first RSV season.

References

1. Sumsuzzman DM, Wang Z, Langley JM, Moghadas SM. Real-world effectiveness of nirsevimab against respiratory syncytial virus disease in infants: a systematic review and meta-analysis. The Lancet Child & Adolescent Health. 2025;9(6):393–403. link
2. Drysdale SB, Cathie K, Flamein F, et al. Nirsevimab for prevention of hospitalizations due to RSV in infants. New England Journal of Medicine. 2023;389(26):2425–2435. link.
3. Hammitt LL, Dagan R, Yuan Y, et al. Nirsevimab for prevention of RSV in healthy late-preterm and term infants. New England Journal of Medicine. 2022;386(9):837–846. link.