The vaccine was about 82% effective at preventing severe cases of the respiratory syncytial virus, or RSV, in infants who’s mothers were immunized, according to phase III of a randomized, double-blind, placebo-controlled study, is regarded as the gold standard of epidemiologic studies.
This level of protection was seen from birth to three months of age. The Pfizer vaccine was still 69% effective against the disease at six months of age, though there was a decline in protection.
Pregnant participants in the study were monitored throughout the vaccination process and for six months following delivery to evaluate the vaccine’s safety and effectiveness. Over half of the infants were monitored for two years, and all were monitored for at least a year.