Respiratory Syncytial Virus Vaccine Candidate Found to Protect Infants Against Severe Illness


Pre-planned safety reviews performed for the duration of the study found that the investigational vaccine is well-tolerated with no safety concerns for both the vaccinated individuals and their newborns.

A novel bivalent respiratory syncytial virus (RSV) prefusion vaccine candidate (RSVpreF or PF-06928316, Pfizer) administered to pregnant women was found to protect their newborns against RSV disease through 6 months after birth.

The novel vaccine candidate was investigated in the phase 3 MATernal Immunization Study for Safety and Efficacy (MATISSE) clinical trial.

The double-blinded, placebo-controlled study investigated the efficacy, safety, and immunogenicity of RSVpreF against medically attended lower respiratory tract illness (MA-LRTI) and severe MA-LTRI in infants born to healthy women who were vaccinated during pregnancy. The study randomized approximately 7400 pregnant individuals 1:1 to receive a single dose of either 120 µg of Pfizer’s RSVpreF or placebo during the late second to third trimester of pregnancy. The investigators also assessed safety throughout the study and immunogenicity of the vaccine in pregnant individuals and their infants.

The participants were tracked for safety through vaccination and for 6 months following delivery. The infants were tracked for at least 1 year to evaluate safety and efficacy, with more than half of the infants followed for 2 years. The study, which began in June 2020, was conducted across 18 countries spanning in the northern and southern hemisphere and in multiple RSV seasons.

The trial achieved 1 of 2 primary endpoints, with the efficacy for severe MA-LRTI at 81.8% through the first 90 days of life. The criteria were not met for the second primary endpoint; however, clinically meaningful efficacy of 57.1% was observed for MA-LRTI in infants from birth through the first 90 days of life. Further, the efficacy for MA-LRTI of 51.3% was observed over the 6-month follow up period.

Pre-planned safety reviews performed for the duration of the study found that the investigational vaccine is well-tolerated with no safety concerns for both the vaccinated individuals and 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, senior vice president and chief scientific officer, Vaccine Research & Development, Pfizer, in a press release. “These data reinforce Pfizer’s resolve to bring our expertise in the research and development of innovative vaccines to address critical public health needs using new approaches and technologies. 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. We would like to thank the pregnant women who volunteered for this trial, along with their infants, and all the investigators around the world who participated in the study for their contribution to this landmark research.”


Pfizer Announces Positive Top-Line Data of Phase 3 Global Maternal Immunization Trial for its Bivalent Respiratory Syncytial Virus (RSV) Vaccine Candidate. Pfizer. November 1, 2022. Accessed November 2, 2022.

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