Pfizer announces positive phase 3 data for RSV vaccine

Pfizer announced positive data from a phase 3 trial on a bivalent RSV vaccine.

Pfizer Inc has announced positive results of a phase 3 trial for vaccination against respiratory syncytial virus (RSV), RSVpreF.

The vaccine met 1 of 2 primary endpoints, showing substantial efficacy of69.4% in infants during the 6-month follow-up period. Statistical success was not met, but 57.1% meaningful efficiency was seen in infants from birth for the first 90 days of life, and 51.3% for infants observed throughout the follow-up period.

Safety reviews also determined tolerance toward the vaccine in vaccinated individuals and their newborns. The vaccine is the first indicated to protect newborns against severe RSV from birth, and Pfizer plans to submit a first regulatory application to the US Food and Drug Administration before the end of 2022.

About 7,400 pregnant individuals were enrolled in the study. Participants were randomized 1:1 to receive either 1 dose of the RSVpreF vaccine or a placebo. Administration took place during either the second or third trimester of pregnancy, with follow-up taking place throughout the 6 months following delivery.

Immunogenicity of the vaccine was tested in maternal patients and their infants to assess safety, and infants were followed for 1 year or more to examine safety and efficiency, with over 50% of infants followed for 2 years. The study took place in 18 countries and began in June 2020, allowing it to span multiple RSV seasons.

RSV affects the lungs and breathing passages, making it potentially life-threatening in some infants. About 2.1 million outpatients and 58,000 hospitalizations occur annually in United States children aged less than 5 years due to RSV. RSV also causes death in 102,000 worldwide per year, and about half of those infants are aged under 6 months old.

Pfizer’s vaccine could be the first maternal vaccine for protection against RSV. Results from the trial will be submitted for peer review in a scientific journal.


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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