Nirsevimab found Effective in Preventing RSV-Associated Hospitalizations Among Infants in new research

In a significant development in pediatric healthcare, nirsevimab, a long-acting monoclonal antibody, has demonstrated robust real-world effectiveness in protecting infants against respiratory syncytial virus (RSV)-associated hospitalizations, according to an analysis by the New Vaccine Surveillance Network during the period of October 1, 2023, to February 29, 2024.

The report was published in CDC Morbidity and Mortality Weekly Report.

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RSV is a major cause of infant hospitalization in the U.S. Nirsevimab, a long-acting antibody, is recommended by CDC for infants and at-risk children. Clinical trials show high efficacy. This analysis provides the first U.S. estimate of post-introduction nirsevimab effectiveness in infants' first RSV season. The CDC's Advisory Committee on Immunization Practices had earlier recommended nirsevimab for infants under the age of 8 months and for children aged 8–19 months at an increased risk for severe RSV disease. This groundbreaking antibody, known for its extended duration of action, emerged from phase 3 clinical trials with an 81% efficacy against RSV-associated lower respiratory tract infections leading to hospitalization within 150 days after receipt.

In the real-world setting, the New Vaccine Surveillance Network's analysis focused on 699 infants hospitalized with acute respiratory illness during the specified period. Among them, 8% (59 infants) had received nirsevimab at least 7 days before the onset of symptoms.

Findings:

• The findings revealed an impressive 90% effectiveness of nirsevimab against RSV-associated hospitalizations (95% CI = 75%–96%).
• Notably, the median time from receipt to symptom onset was 45 days (IQR = 19–76 days).
• Despite the limited number of infants in the analysis who received nirsevimab and the restricted interval data, the early estimate strongly supports the current recommendation for nirsevimab's use in preventing severe RSV disease in infants.

The data underscore the importance of timely intervention with nirsevimab, either through maternal RSV vaccination or direct administration to infants. It is essential to note that the number of infants in the analysis who received nirsevimab was relatively low, making it impractical to stratify the data by the duration from receipt. However, the analysis acknowledges that nirsevimab effectiveness is anticipated to decline with increasing time after receipt due to antibody decay. Continued monitoring and further research will be crucial to refining recommendations and understanding the long-term efficacy of nirsevimab in preventing RSV-associated hospitalizations.

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This breakthrough in pediatric healthcare offers a promising avenue for safeguarding infants against the leading cause of hospitalization in the United States. As the medical community awaits additional data and comprehensive assessments, the current findings affirm the potential of nirsevimab to reshape the landscape of RSV prevention, offering hope for a healthier start in life for countless infants.

Further reading: Moline HL, Tannis A, Toepfer AP, et al. Early Estimate of Nirsevimab Effectiveness for Prevention of Respiratory Syncytial Virus–Associated Hospitalization Among Infants Entering Their First Respiratory Syncytial Virus Season — New Vaccine Surveillance Network, October 2023–February 2024. MMWR Morb Mortal Wkly Rep 2024;73:209–214. DOI: http://dx.doi.org/10.15585/mmwr.mm7309a4