Infants whose mothers received two doses of an mRNA coronavirus vaccine during pregnancy are less likely to be admitted to the hospital for Covid-19 in the first six months of life, according to a new study from the Centers for Disease Control and Prevention. Overall, maternal vaccination was 61 percent effective at preventing infant hospitalization, the researchers found.
Vaccination later in pregnancy — after the first 20 weeks — appeared to provide better protection for infants than earlier vaccination, the study suggests.
The new study is the first real-world, epidemiological evidence that maternal vaccination can protect infants from Covid-19, likely because they are born carrying their mother’s antibodies.
“The bottom line is that maternal vaccination is a really important way to help protect these young infants,” Dr. Dana Meaney-Delman, chief of the Infant Outcomes Monitoring Research and Prevention Branch at the C.D.C., said at a news briefing on Tuesday.
The C.D.C. recommends that women who are pregnant, breastfeeding or trying to become pregnant be vaccinated against Covid-19, which can be dangerous for pregnant women and their children. Research has shown, for instance, that the disease can increase the risk of a variety of pregnancy complications, including preterm birth and stillbirth.
Prior research on other diseases has suggested that women who are vaccinated against other pathogens during pregnancy can pass antibodies to the fetus through the placenta, and scientists have previously found signs that the same antibody transfer might happen after vaccination for Covid-19.
The new study focused on children under six months of age who were admitted to one of 20 U.S. pediatric hospitals between July 1 and Jan. 17. Of the 379 infants included in the study, 176 had been admitted for Covid-19 or had symptoms of the disease; all of these children tested positive for the virus. The remaining 203 children tested negative for the virus.
Among the infants with Covid-19, 16 percent of mothers had been vaccinated during pregnancy, compared to 32 percent of the mothers of hospitalized children without the virus.
Vaccination during the first 20 weeks of pregnancy was 32 percent effective against Covid-19-related hospitalization for infants, the researchers found, whereas later vaccination was 80 percent effective.
But because of the relatively small sample size, more research is needed to determine the optimal timing of vaccination during pregnancy and whether a booster during pregnancy might provide similar protection for infants whose mothers have already received their first set of shots.
“For right now, we want to ensure that we are protecting both the mom and the infant, and so as soon as a pregnant woman is willing to be vaccinated, we recommend that she go ahead and do so,” Dr. Meaney-Delman said.
She added, “Unfortunately, vaccination of infants younger than six months old is not currently on the horizon.”
The study was also not large enough to determine whether maternal vaccination was equally protective against Delta, which was the dominant variant when the study began, and Omicron, which had displaced Delta by the time the research ended.