Pfizer RSV vaccine 82% effective vs severe infection in infants, final data shows

On April 5th, Pfizer announced that their experimental respiratory syncytial virus (RSV) vaccine was 82% effective in preventing severe infections in infants. The vaccine was given to expecting mothers during the second half of their pregnancy, and the trial results confirmed preliminary data from the study. Final data was published in the New England Journal of Medicine, and the vaccine is currently under review by health regulators in both the United States and Europe. The U.S. Food and Drug Administration (FDA) is expected to make a decision on its use by August. If approved, it could be the first maternal vaccine available to prevent RSV disease in infants.

Sanofi and AstraZeneca are also developing a single-dose antibody, nirsevimab, for RSV prevention in infants, which is also under FDA review.

Pfizer’s vaccine, RSVpreF, met one of the two main goals of the late-stage study, showing that it was nearly 82% effective in preventing severe lower respiratory tract illness, such as very low oxygen levels or need for ventilator support, in infants in the first 90 days of life. Severe illness occurred within three months in six infants whose mothers received the vaccine, compared with 33 infants from the placebo group who contracted serious RSV infections. The company evaluated 3,570 infants as part of the study. The shot was 69.4% 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.

However, the shot failed to meet a second main goal of reducing non-severe illness in infants. According to government data, about 58,000 to 80,000 children younger than 5 years old are hospitalized due to RSV infection every year in the United States, and infants are among those at greatest risk for severe illness.