Results from a prespecified pooled analysis of the pivotal MELODY Phase III and Phase IIb trials showed AstraZeneca and Sanofi’s nirsevimab demonstrated an efficacy (relative risk reduction versus placebo) of 79.5% (95% Confidence Interval [CI] 65.9 to 87.7; P<0.0001) against medically attended lower respiratory tract infections (LRTI), such as bronchiolitis or pneumonia, caused by respiratory syncytial virus (RSV) in infants born at term or preterm entering their first RSV season. The pooled analysis studied healthy preterm and term infants who received the optimised dose of nirsevimab compared to placebo through Day 151 and showed an efficacy of 77.3% (95% CI 50.3, 89.7; P<0.001) against RSV LRTI hospitalisations.

In a separate pooled post-hoc analysis of the trials, blood samples taken from infants dosed with nirsevimab exhibited RSV neutralising antibodies that were approximately 50-fold higher than baseline at Day 151 postdose. RSV neutralising antibody levels remained greater than 19-fold higher than placebo recipients with no known RSV infection through Day 361, suggesting protection may extend beyond Day 151.

These findings contribute to the growing body of evidence that nirsevimab has the potential to protect all infants entering their first RSV season with a single dose.

Eric Simões, MD, Clinical Professor, Pediatrics-Infectious Diseases, UC Denver School of Medicine, said: “Respiratory syncytial virus remains the most common cause of lower respiratory tract infection in infants and results in seasonal epidemics globally each year. These new analyses strengthen nirsevimab’s potential to protect all infants across the respiratory syncytial virus season with a single dose, which may lead to a paradigm shift in respiratory syncytial virus prevention.”

Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca, said: “Each year, respiratory syncytial virus causes seasonal epidemics of lower respiratory tract infections in infants. These analyses add to nirsevimab’s compelling body of evidence as the first potential single-dose preventative immunisation for all infants against respiratory syncytial virus, addressing a clear unmet need in the respiratory syncytial virus preventative landscape.”  

Jean-François Toussaint, Global Head of Research and Development Vaccines, Sanofi, said: “These new analyses are very consistent with and confirm the strong results observed in all Phase II and Phase III studies that evaluated nirsevimab in diverse paediatric populations. We take pride in the progress made to develop a potential solution to address this long unmet need for all infants.”

The overall safety profile of nirsevimab in the two trials have previously been reported, and no clinically meaningful differences in safety results were seen between the nirsevimab and placebo groups.

The data are being presented at the 40th Annual Meeting of the European Society for Paediatric Infectious Diseases (ESPID) from 9th-13th May in Athens, Greece.

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