Researchers examined the effectiveness of nirsevimab during the 2024–2025 RSV season using a large, multi-institutional dataset.


RT’s Three Key Takeaways:

  1. Large-Scale Evidence — In over 409,000 infants, those who received nirsevimab had markedly fewer RSV-related hospitalizations than untreated peers.
  2. Hospitalization Risk Reduction — Only 0.4% of treated infants were hospitalized versus 1.2% untreated; hazard ratios showed a 71–77% lower risk with nirsevimab.
  3. Respiratory Protection Confirmed — Nirsevimab consistently reduced severe RSV illness requiring hospital care, reinforcing its role as a key tool to protect infant lungs during RSV season.


According to data published in JAMA Network Open, infants treated with nirsevimab had a significantly lower rate of hospitalization for RSV compared to untreated infants.1

A retrospective cohort analysis using the Epic Systems Cosmos database, which includes data from more than 300 million patients across diverse healthcare systems.1 The primary outcome was RSV-associated hospitalization, and exposure was receipt of nirsevimab.1

A total of 409,723 infants were included in the analysis; among these, 194,422 (47.5%) received nirsevimab. The treated and untreated groups were similar in demographics, with a median age of 8 months and roughly equal sex distribution.1

According to results, striking differences emerged in hospitalization outcomes: only 0.4% (850 infants) of the treated group experienced RSV-associated hospitalization, compared with 1.2% (2,535 infants) in the untreated group (P < .001). Data also indicated that peak daily hospitalization rate was significantly lower among treated infants (2.90 per 100,000) compared to the untreated cohort (13.84 per 100,000).1

Cox proportional hazards models confirmed these findings. The unadjusted hazard ratio for RSV-associated hospitalization in treated infants was 0.29 (95% CI, 0.26–0.32), and the adjusted hazard ratio was 0.23 (95% CI, 0.21–0.26), demonstrating that nirsevimab was associated with a 71–77% reduction in hospitalization risk.1

Researchers report this is the first large-scale cohort study of nirsevimab during the 2024–2025 RSV season, with a sample size larger than recent meta-analyses.1 The findings align with earlier evidence from the 2023–2024 season, confirming consistent effectiveness across years.1

The authors note limitations, including potential underestimation of vaccine exposure, missed doses outside participating facilities, and loss to follow-up. Nonetheless, the results strongly support nirsevimab as an effective preventive strategy against RSV hospitalization.1

Researchers concluded that nirsevimab substantially reduced the risk of RSV-associated hospitalization in infants and should remain an RSV prevention method.1

  1. Pelletier JH, Rush SZ, Robinette E, et al. Nirsevimab Administration and RSV Hospitalization in the 2024-2025 Season. JAMA Netw Open. 2025;8(9):e2533535. doi:10.1001/jamanetworkopen.2025.33535