A new study published in Pediatrics has found that nirsevimab, a monoclonal antibody, is 76% effective in preventing medically attended respiratory syncytial virus (RSV)-related lower respiratory tract infections (LRTIs) in infants. Conducted across primary care settings in Spain during the 2023–2024 RSV season, the study provides strong evidence for nirsevimab's real-world effectiveness, both overall and in a targeted catch-up immunization program.1
The study involved 160 infants born after April 1, 2023. Of these, 141 (88%) received nirsevimab, with the majority (79%) administered through a catch-up program outside the hospital setting before RSV season. The infants in the catch-up group showed even higher efficacy, with 80.2% effectiveness in preventing RSV-related LRTIs, compared to 75.8% in the overall study population. Of the infants tested, 44 (27.5%) were found to have RSV, with 37 (28.9%) cases coming from the catch-up group.1
The primary outcome of the study was RSV-related LRTIs that required medical attention. A test-negative design was used to assess nirsevimab's real-world effectiveness, comparing RSV-positive infants with those who tested negative. This approach gave a robust evaluation of the monoclonal antibody’s ability to prevent RSV infections.1
Nirsevimab, a long-acting monoclonal antibody, had previously shown 79% efficacy in clinical trials for preventing medically attended RSV-LRTIs in infants. However, its real-world effectiveness in primary care settings had not been well established until now. These findings confirm nirsevimab as a highly effective tool in reducing RSV-related illness, particularly in outpatient settings.1
The study also underscores the importance of catch-up immunization programs, which can reduce the burden of RSV in primary care settings, especially in regions with high RSV activity. By offering nirsevimab outside hospital settings before RSV season, healthcare providers can proactively reduce medical visits and hospitalizations, easing the strain on healthcare systems during peak RSV season.1
According to the investigators, “This study demonstrates the effectiveness of nirsevimab in preventing medically attended RSV-LRTI in infants under 10 months, both overall and for the catch-up group.” They also highlighted that catch-up administration of nirsevimab could be a crucial strategy for reducing RSV’s impact on healthcare systems.1
What You Need To Know
Nirsevimab demonstrated 76% effectiveness in preventing medically attended RSV-related LRTIs in infants, with higher efficacy (80.2%) in the catch-up immunization group.
Catch-up immunization programs, administering nirsevimab outside hospital settings before RSV season, significantly improved efficacy and helped reduce medical visits and hospitalizations.
The study provides real-world evidence supporting nirsevimab's effectiveness in primary care settings, confirming its ability to prevent RSV infections and align with results from earlier clinical trials.
The findings are further supported by another recent real-world study Contagion covered, published in The Lancet, which analyzed nirsevimab’s effectiveness in preventing RSV-related hospitalizations in infants. Conducted as part of the NIRSE-GAL research in Spain, this study found that nirsevimab reduced hospitalizations for RSV in infants under 6 months of age by 82% compared to infants who received no RSV intervention. The study involved 9,408 infants, with only 30 hospitalizations for RSV-related LRTI among those who received nirsevimab, compared to 16 hospitalizations among 851 unvaccinated infants.2
In total, 9,408 infants received nirsevimab during the study period, and only 30 of these infants were hospitalized for RSV-related LRTI, compared to 16 hospitalizations among 851 infants who did not receive the immunization. The study further confirms that nirsevimab can substantially reduce RSV hospitalizations, including severe cases requiring oxygen.3
These interim results from the NIRSE-GAL study further validate nirsevimab’s role in reducing severe RSV disease, including cases requiring oxygen. The study also confirms the real-world effectiveness of nirsevimab, supporting earlier findings from clinical trials, such as the HARMONIE phase 3b study.3 With FDA approval for nirsevimab’s use in infants born during or entering their first RSV season, as well as in children up to 24 months of age who remain vulnerable to severe RSV disease, these new results reinforce the monoclonal antibody’s key role in protecting infants during RSV season.2
Both studies provide real-world evidence supporting nirsevimab's effectiveness, though they differ in study design, population, and the outcomes they assess (hospitalizations vs. medical visits). Together, these studies show that nirsevimab is effective in preventing RSV infections in infants, particularly when used as part of a catch-up immunization program. Its ability to reduce hospitalizations and severe RSV disease suggests it could help reduce the impact of RSV on both infants and healthcare systems, particularly during RSV season.
References
1. López-Lacort M, Muñoz-Quiles C, Mira-Iglesias A, et al. Nirsevimab effectiveness against severe respiratory syncytial virus infection in the primary care setting. Pediatrics. 2024; e2024066393. doi:10.1542/peds.2024-066393.
2. Press Release: Beyfortus real-world evidence published in The Lancet shows 82% reduction in infant RSV hospitalizations. Sanofi. News release. May 2, 2024. Accessed December 4 2024.
https://www.sanofi.com/en/media-room/press-releases/2024/2024-05-02-05-00-00-2873804
3. Ares-Gomez S, Mallah N, Santiago-Perez M, et al. Effectiveness and impact of universal prophylaxis with nirsevimab in infants against hospitalisation for respiratory syncytial virus in Galicia, Spain: initial results of a population-based longitudinal study. Lancet. Published online April 30, 2024. Accessed December 4, 2024. doi:10.1016/S1473-3099(24)00215-9
