SCOTT DETROW, HOST:
RSV is the most common reason why babies end up in the hospital in the first year of their life. The virus can cause serious breathing issues. Now the largest real-world study to date finds that an RSV vaccine given to expectant mothers is more effective at protecting babies than previously shown. NPR's Maria Godoy has more.
MARIA GODOY, BYLINE: Dr. Naima Joseph is a maternal fetal medicine specialist with Boston University. She's also the mom of twins who contracted RSV shortly after they were born in 2021.
NAIMA JOSEPH: I saw that with my kids - trouble breathing, gasping for air, low oxygen levels and needing oxygen support in the hospital.
GODOY: Her twins recovered, and in the years since, two options have become available to immunize babies against RSV. One is a maternal vaccine. In the U.K., the government offered the shot free of charge to all pregnant women in their third trimester, beginning in the fall of 2024 at the start of RSV season. That maternal vaccination dramatically cut the risk that babies ended up in the hospital, says Matt Wilson of the UK Health Security Agency.
MATT WILSON: What we found is that, as long as there is at least two weeks between vaccination and birth, we get this kind of 80% effect, 80% reduction.
GODOY: Previous clinical trials had shown the maternal vaccine to be about 70% effective. In a new study, Wilson and his colleagues looked at outcomes for some 289,000 babies born between September 2024 and March 2025. They found that timing matters. Giving mothers the shot at least four weeks before birth offered even stronger protection because antibodies had more time to transfer to the fetus. But even when mothers got the shot just 10 days before giving birth, hospitalizations from RSV dropped by half.
WILSON: So what that means is if someone's not vaccinated early on in pregnancy and then towards the end of pregnancy there is an opportunity to do so, it's really worth doing so.
GODOY: Wilson presented the findings at the meeting of the European Society of Clinical Microbiology and Infectious Diseases. Dr. Naima Joseph says the findings offer lessons for the U.S., where infants can be immunized either through the maternal RSV vaccine or with a monoclonal antibody shot given to newborns. While uptake has improved for both options...
JOSEPH: We're still seeing a large number of people who just have no protection. And so that means that there is some gap to fill, and maybe maternal immunization might be that way to do that.
GODOY: She says all those prenatal visits to the OB offer lots of opportunities to encourage expectant moms to get the vaccine and protect their babies against RSV. Maria Godoy, NPR News.
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