This pivotal Phase 3 study will determine if MEDI8897 will prevent medically attended RSV-confirmed lower respiratory tract infections (LRTI) in healthy infants entering their first RSV season.

The population to be enrolled is healthy late preterm and term infants born 35 weeks 0 days or greater gestational age (GA) who would not be eligible to receive RSV prophylaxis.

A total of approximately 3,000 infants will be randomized 2:1 to receive either MEDI8897 or a placebo.

All subjects will be followed for approximately 510 days after dosing. Enrollment is planned at approximately 350 sites across the USA, Canada, Europe, Asia, and Southern Hemisphere.

Results

AstraZeneca presented two analyses at the European Society for Paediatric Infectious Diseases meeting.

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. 

In a separate pooled post-hoc analysis of the trials, blood samples taken from infants dosed with nirsevimab exhibited RSV neutralizing antibodies that were approximately 50-fold higher than baseline at Day 151 postdose. RSV neutralizing 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.