The use of monoclonal antibody nirsevimab (Beyfortus) in protecting young infants from hospitalization due to respiratory syncytial virus (RSV) has been a topic of discussion in the medical community. The French prospective ENVIE study conducted by Naim Ouldali, MD, PhD, and colleagues has shed light on the effectiveness of nirsevimab in preventing RSV-related hospital admissions, pediatric intensive care unit (PICU) admissions, and mechanical ventilation in infants.
Study Findings
According to the study published in the New England Journal of Medicine, nirsevimab was estimated to be 83% effective in preventing hospitalization from RSV bronchiolitis in infants younger than 12 months of age. The effectiveness of nirsevimab was 69.6% against RSV bronchiolitis leading to PICU admission and 67.2% against RSV-associated bronchiolitis requiring ventilatory support. The authors of the study highlighted the significant impact of nirsevimab prophylaxis in reducing hospitalizations among infants with severe RSV cases.
Researchers also observed a lower effectiveness of nirsevimab in preventing hospitalization among infants with at least one risk factor for bronchiolitis. The study reported an effectiveness rate of 64.8% in this subgroup, although the absolute numbers were small. However, the overall effectiveness of nirsevimab appeared to be consistent among infants younger than 3 months and older infants.
Comparison with Previous Studies
The study results were compared with the findings of prelicensure phase III trials such as the MELODY trial and the HARMONIE trial. While the MELODY trial showed a lower efficacy of 74.5% in preventing RSV-related lower respiratory tract infections, the HARMONIE trial demonstrated an efficacy of about 83% in preventing RSV hospitalizations, consistent with the ENVIE study results. The differences in effectiveness were attributed to the timing of outcome assessment, with nirsevimab effectiveness possibly decreasing over time.
Natasha Halasa, MD, MPH, emphasized the importance of ensuring widespread access to nirsevimab, especially in low- and middle-income countries where a majority of RSV-attributable deaths occur. The study authors recommended starting annual nirsevimab campaigns at the beginning of the RSV outbreak, similar to influenza vaccination programs, to maximize the program’s impact.
In the United States, the Food and Drug Administration (FDA) approved nirsevimab for passive immunization in infants against RSV in July 2023. The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices issued recommendations for nirsevimab use in August 2023, recommending a single dose for infants younger than 8 months.
Study Limitations
The authors acknowledged several limitations of the ENVIE study, including its observational case-control design, which prevented causal conclusions. The assessment of nirsevimab effectiveness was conducted early after the initiation of the free-of-charge nirsevimab campaign in France, leading to a relatively short evaluation period. Shortages of nirsevimab during the program may have resulted in differential access among socioeconomic groups, potentially introducing bias. Subgroup analyses were underpowered and exploratory in nature, according to the authors.
The ENVIE study provides valuable insights into the effectiveness of nirsevimab in preventing RSV-related hospitalizations in infants. The findings support the use of nirsevimab as a prophylactic measure against severe RSV cases, with potential implications for public health strategies and vaccination campaigns. Further research and surveillance are needed to assess the long-term impact of nirsevimab and optimize its use in at-risk populations.