Maternal RSV Vaccine Prevents Infection in Infants, Pfizer Announces

The Pfizer investigational maternal vaccine against respiratory syncytial virus (RSV) has been shown to protect against the disease in infants through the first 90 days of life, according to a company announcement made Tuesday.

The positive top-line data come from the global phase 3 MATISSE  (MATernal Immunization Study for Safety and Efficacy) trial in which Pfizer is investigating the efficacy of its bivalent RSV prefusion vaccine candidate, RSVpreF or PF-06928316, to protect infants after birth when the shot is given to pregnant women.

According to the company, RSVpreF efficacy was 81.8% (CI: 40.6%-96.3%) against severe medically attended lower respiratory tract illness (MA-LRTI) in infants through the first 90 days of life and it remained high (69.4% [(CI: 44.3%-84.1%]) through the first 6 months of follow-up.

The trial also found clinically meaningful efficacy of 57.1% for nonsevere MA-LRTI among infants from birth through the first 90 days of life, which declined to 51.3% (CI: 29.4%-66.8%) over the 6-month follow up period.

No safety concerns were reported for either vaccinated mothers or their newborns.

“We are thrilled by these data as this is the first-ever investigational vaccine shown to help protect newborns against severe RSV-related respiratory illness immediately at birth,” said Annaliesa Anderson, PhD, Pfizer senior vice president and chief scientific officer, in Pfizer’s announcement.

“We look forward to working with the FDA and other regulatory agencies to bring this vaccine candidate to expectant mothers to help protect their infants against severe RSV during their most vulnerable first six months of life, which has the highest burden of RSV illness in infants.”

If approved, the vaccine could have significant impact on RSV prevalence in the US and throughout the world, observed Eric AF Simões, MD, clinical professor, pediatrics-infectious diseases, University of Colorado School of Medicine and Children’s Hospital Colorado, Aurora. “Every year we see high levels of RSV cases among babies in the US, with some regions reporting hospital admission rates higher than normal this year.” A maternal vaccine with high efficacy among newborns could substantially reduce the burden of severe disease through infants’ first 6 months of life, added Simões.

If approved, the vaccine could have significant impact on RSV prevalence in the US and throughout the world, observed Eric AF Simões, MD, clinical professor, pediatrics-infectious diseases, University of Colorado School of Medicine and Children’s Hospital Colorado, Aurora.

Having met 1 of the study protocol’s prespecified regulatory success criteria, Pfizer, on guidance from the independent data monitoring committee and in consultation with the US Food and Drug Administration, has stopped further trial enrollment.

The FDA granted RSVpreF breakthrough status in March 2022 and in April Pfizer published results from the phase 2b portion of MATISSE which demonstrated that infants born to mothers who received the vaccine acquired antibodies through the placenta.

Pfizer said it plans to submit a biologics license application to the FDA for RSVpreF by year’s end.

MATISSE enrolled approximately 7,400 pregnant women aged ≤49 years of age who were randomized in a 1:1 ratio to receive a single dose of either 120 µg of Pfizer’s RSVpreF or placebo during the late second to third trimester of their pregnancy. Participants were followed for safety through vaccination and 6 months post-partum. Infants were followed for ≥1 year for safety and efficacy, with over half of the infants followed for 2 years. MATISSE was initiated in June 2020 in 18 countries and so spanned multiple RSV seasons in both the northern and southern hemisphere.