Pfizer’s experimental respiratory syncytial virus (RSV) vaccine was 82 percent effective in preventing severe infections in newborns when given to expectant mothers in the second half of pregnancy, according to trial details released Wednesday that support preliminary study data.
Final data from the study, which was stopped early when the vaccine was found to be effective, was published in the New England Journal of Medicine.
Pfizer released the results of a preliminary trial of the vaccine in November, which is currently under review by health regulators in both the United States and Europe. The US Food and Drug Administration is expected to rule on its use by August.
FDA approval could make Pfizer’s vaccine the first maternal vaccine to prevent the disease in infants.
Sanofi and AstraZeneca are developing a single-dose antibody, nirsevimab, to prevent RSV in infants, which is also under FDA review.
Pfizer’s vaccine, RSVpreF, met one of the two main objectives of the late-stage study. It was nearly 82 percent effective in preventing severe lower respiratory tract illnesses, such as very low oxygen levels or needing ventilator support, in infants in their first 90 days of life.
Pfizer said severe illness developed within three months in six infants whose mothers received the vaccine, compared with 33 infants in the placebo group who developed serious RSV infections. The company evaluated 3,570 infants in the study.
The shot was 69.4 percent effective in preventing severe infections in the first 180 days. Severe illness occurred within six months in 19 infants born to mothers in the vaccine group, compared with 62 infants in the placebo group.
The shot failed to achieve the second key goal of reducing non-severe illnesses in newborns.
According to government data, about 58,000 to 80,000 children under the age of five are hospitalized each year in the United States due to RSV infection, and infants are at greatest risk for severe disease.