A vaccine given during pregnancy that prevents respiratory syncytial virus (RSV) in infants was about 66% effective at protecting against RSV-associated respiratory illness, and about 69% effective at protecting against severe disease, according to a study in the New England Journal of Medicine. The came from a randomized clinical trial involving more than 5000 pregnant people and their infants in 24 countries.
However, the researchers stopped the trial early because of an increased risk of preterm births. About 7% of infants whose birthing parent had received the vaccine were born before 37 weeks compared with roughly 5% of infants whose birthing parent had received a placebo. The higher rate of preterm births was 鈥減redominantly observed鈥� among low- and middle-income countries between August and December 2021, and was not explained by SARS-CoV-2 infection or COVID-19 vaccination, the researchers noted.
The maternal vaccine evaluated in the study is similar to Abrysvo, which the US Food and Drug Administration (FDA) . The FDA-approved vaccine is currently being monitored for vaccine-associated risks including preterm births. Despite the potential risks of maternal RSV vaccination, 鈥渋t is essential to weigh this small risk against the proven benefits,鈥� the authors of a linked wrote, adding that most of the preterm births occurred between 34 and 37 weeks.
Published Online: April 12, 2024. doi:10.1001/jama.2024.5155