Efficacy of Nirsevimab in Preventing RSV-Related Illness in Infants

Recent research has established that nirsevimab significantly protects infants from lower respiratory tract disease associated with respiratory syncytial virus (RSV). This finding was published in the journal Pediatrics on July 22, 2025.

The study, conducted by a team at the Kaiser Permanente Vaccine Study Center in Oakland, California, assessed the effectiveness of nirsevimab against RSV-related health complications during the 2023-2024 RSV season. The investigation included a cohort of 31,900 infants, with nearly half (49.1%) receiving the nirsevimab treatment.

The researchers noted a stark contrast in RSV LRTD episodes between infants who were immunized with nirsevimab and those who were not. Specifically, they documented 35 episodes among the nirsevimab-immunized group compared to 462 episodes in the non-immunized group, translating to rates of 6.10 and 58.51 cases per 1,000 person-years, respectively.

In terms of effectiveness, nirsevimab demonstrated remarkable results, showing an effectiveness rate of 87.2% against RSV LRTD, 98.0% against hospitalized RSV LRTD, and 71.0% against PCR-confirmed RSV cases. Additionally, the study highlighted that infants administered nirsevimab experienced fewer healthcare encounters and significantly lower odds of hospitalization due to RSV LRTD.

The findings strongly support the recommendations made by the Advisory Committee on Immunization Practices, advocating that infants under 8 months old entering their first RSV season should receive nirsevimab to mitigate the risk of RSV infection.

This critical research underscores the importance of preventive measures in safeguarding infant health during the RSV season and aims to reduce the burden of this common but serious viral infection.