Topline data were announced from a phase 3 trial evaluating the efficacy and safety of maternal immunization with RSVpreF (PF-06928316), a bivalent respiratory syncytical virus (RSV) vaccine candidate, against medically attended lower respiratory tract illness (MA-LRTI) and severe MA-LRTI due to RSV in infants.

The RSVpreF vaccine candidate consists of 2 prefusion F proteins selected to optimize protection against RSV A and B. The randomized, double-blind, placebo-controlled MATISSE trial ( Identifier: NCT04424316) enrolled approximately 7400 pregnant individuals (≤49 years of age) who were between 24 and 36 weeks of gestation. Patients were randomly assigned 1:1 to receive a single dose of either RSVpreF or placebo during the late second or third trimester of their pregnancy.

Interim results showed vaccine efficacy of 81.8% (CI, 40.6-96.3) against severe MA-LRTI in infants from birth through the first 90 days of life. Efficacy of 69.4% (CI, 44.3-84.1) was observed over the 6-month follow-up period. 

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While the second primary endpoint did not meet statistical significance, vaccine efficacy against MA-LRTI was reported to be 57.1% (CI, 4.7-79.8) in infants from birth through the first 90 days of life and 51.3% (CI, 29.4-66.8) over the 6-month follow up period. No safety concerns were noted for the vaccinated individuals or the infants.

Pfizer has decided to stop enrollment in the study based on the recommendation of the data monitoring committee and in consultation with the Food and Drug Administration. The Company plans to submit a Biologics License Application (BLA) to the FDA by the end of 2022. The Agency previously granted Breakthrough Therapy designation to RSVpreF for this indication.


Pfizer announces positive top-line data of phase 3 Global Maternal Immunization Trial for its bivalent respiratory syncytial virus (RSV) vaccine candidate. New York, NY. News release. Pfizer. Accessed November 1, 2022.

This article originally appeared on MPR