AstraZeneca and Sanofi's antibody prevents RSV in phase 3, accelerating path to market

AstraZeneca and Sanofi’s nirsevimab has protected healthy babies against respiratory syncytial virus (RSV) disease in a phase 3 clinical trial. The earlier-than-expected readout will enable a 2022 filing for a monoclonal antibody Sanofi CEO Paul Hudson has hailed as a “massive opportunity.”
Investigators randomized around 1,500 healthy late preterm and term infants to receive either one dose of half-life extended antibody nirsevimab or placebo. Over the 150 days after treatment, the incidence of medically attended RSV-confirmed lower respiratory tract infections was lower in the nirsevimab arm than the control group, causing the study to hit its primary endpoint.

The researchers are yet to share data from the trial. In an earlier phase 2b study, nirsevimab reduced infections by 70% and related hospitalizations by 78%. AstraZeneca and Sanofi said the safety profile in the phase 3 was consistent with earlier data and didn’t differ from placebo in clinically meaningful ways.

Investigators are enrolling an additional 1,500 infants to complete the safety evaluation. Even so, the earlier-than-expected efficacy data will enable the partners to bring forward regulatory submissions to 2022, rather than the originally targeted 2023.

If approved, nirsevimab will give physicians a new approach to RSV. Swedish Orphan Biovitrum's monthly vaccine Synagis is already available for high-risk babies, and GlaxoSmithKline is working on a maternal vaccine that entered phase 3 late last year. Nirsevimab is different as it is designed to be given once to all infants at birth or the start of the RSV season.

AstraZeneca and Sanofi are putting nirsevimab up against Synagis in another phase 2/3 clinical trial. That study is evaluating the products in preterm infants and children with chronic lung disease and congenital heart disease entering their first and second RSV seasons. The partners now expect data from the study in the coming months, again ahead of schedule.  

Sanofi paid €120 million ($145 million) for a 50% stake in nirsevimab, then known as MEDI8897, in 2017 as part of a deal that saw it commit to up to €495 million in development and sales milestones. The asset remained a focus throughout the reprioritization of Sanofi’s pipeline. Hudson called the drug a “massive opportunity” for Sanofi in January.