Mothers who get the Covid-19 vaccine during pregnancy likely protect their babies from hospitalization due to the virus when they are born, according to the Centers for Disease Control and Prevention.

Babies younger than 6 months were 61% less likely to be hospitalized with Covid if their mothers received the two-dose vaccine from Pfizer or Moderna during pregnancy, according to a study published Tuesday in the Morbidity and Mortality Weekly Report of the CDC.

Maternal vaccination later in pregnancy, from 21 weeks to 14 days before delivery, was associated with an even higher level of protection, 80%, for the baby against hospitalization for covid.

Dr. Dana Meaney-Delman, chief of the CDC's infant outcomes branch, said the study suggests that antibodies transferred from the mother to the developing fetus protect the newborn against Covid.

"Unfortunately, vaccinating infants younger than 6 months is not on the horizon at this time, which highlights why vaccination during pregnancy is so important for these young babies," Meaney-Delman told reporters during a conference call Tuesday. .

Previous research, published in the American Journal of Obstetrics and Gynecology, found that antibodies from the mother of the Covid vaccine are transferred through the placenta to the developing fetus. The CDC study provides real evidence that antibodies protect newborns.

The vast majority of babies, 84%, hospitalized with covid in the study were born to unvaccinated mothers. The study examined 379 babies at 20 children's hospitals in 17 states from July through January. The babies were divided into two groups, 176 who had covid and 203 who did not. Sixteen percent of mothers of Covid-positive babies were fully vaccinated, while 32% of mothers of Covid-negative babies were fully vaccinated.

The CDC said the study had some limitations. It did not test whether the mothers tested positive or negative for Covid before or during pregnancy, nor did it analyze the effectiveness of the vaccine against specific variants. It is also unclear whether other differences in behavior between vaccinated and unvaccinated mothers contributed to the risk of infection for their newborns.

The CDC recommends that women who are pregnant, planning to become pregnant, or breastfeeding get vaccinated against Covid. People who are currently or recently pregnant are at increased risk of severe illness from Covid, according to the CDC.