Nirsevimab 90% Effective Against RSV Hospitalization among Infants, According to New CDC Data

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Nirsevimab (Beyfortus, AstraZeneca and Sanofi) was 90% effective at preventing respiratory syncytial virus (RSV)-associated hospitalization in infants during their first RSV season, according to new real-world data from the US Centers for Disease Control and Prevention (CDC).

“This finding supports current CDC recommendations that all infants should be protected by maternal RSV vaccination or infant receipt of nirsevimab, to reduce the risk for RSV-associated hospitalization in their first RSV season,” wrote researchers in the CDC’s Morbidity and Mortality Weekly Report released March 7, 2024.

RSV is the leading cause of hospitalization among infants in the US, and in August 2023, the CDC’s Advisory Committee on Immunization Practices recommended nirsevimab for infants aged <8 months to protect against RSV-associated lower respiratory tract disease during their first RSV season and for children aged 8-19 months who are at increased risk for severe RSV.

With this current RSV season being the first time that the monoclonal antibody is available, the analysis “provides the first US estimate for post-introduction nirsevimab effectiveness among U.S. infants during their first RSV season,” wrote first author Heidi Moline, MD, of the CDC’s National Center for Immunization and Respiratory Practices, and colleagues.

Using data from the New Vaccine Surveillance Network, Moline and coauthors examined the effectiveness of nirsevimab in a sample of 699 infants hospitalized with acute respiratory illness (ARI) at 4 US sites (Pittsburgh, Seattle, Houston, and Nashville) during their first RSV season between October 1, 2023, and February 24, 2024.

Among the cohort, there were 407 participants who received a positive RSV test result (ie, case-patients) and 292 who received a negative RSV test result (ie, control patients), according to investigators.

Overall, 1% (n=6) of case-patients received nirsevimab, as compared with 18% (n=53) of control patients. Among the cohort, receipt of nirsevimab ranged from 4% to 12% by site, added researchers. Results showed that a greater proportion of infants with high-risk medical conditions received nirsevimab (46%) compared with those without those conditions (6%).

In addition, investigators noted that nirsevimab was 90% effective against RSV-associated hospitalization, with a median time of 45 days from receipt of the drug to ARI symptom onset.

“Although nirsevimab uptake and the interval from receipt of nirsevimab were limited in this analysis, this early estimate supports the current nirsevimab recommendation for the prevention of severe RSV disease in infants,” concluded Moline et al.

Source: 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. Morbidity and Mortality Weekly Report. 2024;73:209-214. doi: 10.15585/mmwr.mm7309a4