Pfizer's Maternal RSV Vaccine Protects Newborns from Severe Disease

Pfizer_Pierre Suu/Getty Images

Pierre Suu/Getty Images

Topline data from Pfizer's Phase III trial of RSVpreF, a bivalent RSV vaccine, demonstrated high efficacy against severe medically attended lower respiratory tract illness (severe MA-lRTI) in infants when given during the late second or third trimester of pregnancy.

In the MATISSE trial, 7,400 pregnant women 49 years of age and younger participated, receiving a single vaccine injection or placebo. 

In the first of two primary endpoints, severe MA-lRTI, the vaccine demonstrated 81.8% efficacy to infants through the first 90 days of life. An efficacy of 69.4% was maintained over a six-month follow-up period.

The second primary endpoint, clinically meaningful efficacy for medically attended cases (doctor visits), was not met. While Pfizer saw a high efficacy readout of 57.1%, the confidence interval was just under the FDA threshold of 20%.

In the United States alone, there are almost 2.1 million doctor visits per year for RSV. If this vaccine were to be approved, it could have a significant decrease in visits, a Pfizer spokesperson, who declined to be named, told BioSpace. 

No safety concerns for the mothers or newborns were observed, and the vaccine was well tolerated.

The trial's Data Monitoring Committee recommended that Pfizer could halt enrollment in the study, and the FDA agreed. Based on the results, the company plans to submit a Biologics License Application to the FDA by the end of the year. This will be followed by submissions to regulators in other countries.

"Every year we see high levels of RSV cases among babies in the U.S. with some regions reporting hospital admission rates higher than normal this year," said Eric A.F. Simões, M.D., clinical professor, pediatrics-infectious diseases, University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, in a statement. 

The vaccine received Breakthrough Therapy Designation from the FDA in March for the prevention of RSV-associated lower respiratory tract disease in infants up to six months of age via active immunization of pregnant women.

That designation was based on data from the Phase IIb proof-of-concept vaccine trial. In November 2018, the FDA granted the vaccine Fast Track designation.

Elsewhere in the RSV pipeline, Pfizer announced positive topline data from an interim analysis for the Phase III RENOIR vaccine trial in adults 60 years and older in August. It is still ongoing.

Back to news