Reviewed by Sanchi Malhotra MD, University of California Los Angeles
This was a population-based surveillance case-control study conducted by the new vaccine surveillance network demonstrating that Nirsevimab (monoclonal pre-F antibody) was effective against medically attended RSV acute respiratory infection and hospitalizations.
Medically attended RSV infections in children under 5 in the 2023-2024 season (after introduction of maternal RSV vaccine and Nirsevimab) were compared to 3 pre-pandemic RSV seasons (2017-2020). RSV seasonality and severity was atypical in 2021-2022 due to the pandemic so those years were excluded. Children under 5 who presented to medical care for acute respiratory infection (ARI) to a study site were included, cases and controls were infants with positive and negative RT-PCR tests for RSV, respectively.
28,689 children in total were enrolled (9,536 during 2023-2024 season and 19,153 in 2017-2020 seasons). RSV-associated hospitalization rates in 2023-2024 were similar to average 2017-2020 seasonal rates at 5.0 (95% CI 4.6-5.3) per 1000 among children younger than 5 years. The highest hospitalization rates were among children 0-2 months (26.6; 95% CI 23.0-30.2).
In the 2023-2024 season, 14% of infants less than 8 months received Nirsevimab, and 4% younger than 6 months at enrollment were born to maternal RSV vaccine recipients.
Nirsevimab effectiveness was 89% (95% CI 79%-94%) against medically attended RSV-associated ARI and 93% (95% CI, 82%-97%) against RSV-associated hospitalization. Unfortunately, Maternal vaccine uptake was too low to study effectiveness.
Overall, only a small fraction of infants in their first RSV season had received Nirsevimab or were born to mothers who received maternal RSV vaccine. This was likely multifactorial including difficulties in the supply and roll out of Nirsevimab and small window for eligible pregnant persons to get vaccinated after approval of maternal vaccine in September 2023. This study may be more informative if repeated after a few years of Nirsevimab and maternal RSV implementation.
Reference:
Moline HL, Toepfer AP, Tannis A, et al. Respiratory Syncytial Virus Disease Burden and Nirsevimab Effectiveness in Young Children From 2023-2024 [published correction appears in JAMA Pediatr. 2025 Feb 1;179(2):223. doi: 10.1001/jamapediatrics.2024.6442.]. JAMA Pediatr. 2025;179(2):179-187. doi:10.1001/jamapediatrics.2024.5572 https://jamanetwork.com/journals/jamapediatrics/article-abstract/2827176