Babies born to mothers fully vaccinated against the coronavirus during pregnancy were around 60% less likely to be hospitalized with severe Covid, a new study by the US Centers for Disease Control and Prevention said on Tuesday.
Such an effect had been hypothesized -- because of the transfer of antibodies through the placenta during pregnancy and through breast milk after birth -- but wasn't backed by real world evidence until now.
The CDC carried out a study involving 379 babies aged up to six months, who were hospitalized in 20 pediatric centers from July 2021 to January 2022.
The authors studied the odds of Covid-19 vaccination among mothers whose babies were hospitalized with the disease (176 infants) compared to the odds of vaccination among mothers whose babies were hospitalized for non-Covid reasons (203 infants), who were a control group.
This is a statistical method used in real world studies to try to examine patients with similar characteristics, and is often used when it's not possible or ethical to carry out a randomized clinical trial.
"Babies less than six months old whose mothers were vaccinated were 61% less likely to be hospitalized with Covid-19," CDC researcher Dana Meaney-Delman said in a press call.
What's more, 84% of babies who were hospitalized with Covid were born to people not vaccinated in pregnancy. The one baby who died in the study was born to a mother who was not vaccinated.
Black and Hispanic babies were disproportionately hospitalized for Covid.
"The bottom line is that maternal vaccination is a really important way to help protect these young infants," said Meaney-Delman.
The study further found that completion of a two-dose vaccine series later in pregnancy was more protective than earlier in pregnancy – 80% compared to 32%.
Although that is consistent with what is known about the waning of antibody levels in the months that follow vaccination, Meaney-Delman said it was important for people to get vaccinated at any stage during pregnancy in order to protect both the mother and baby.
"If we have a woman who comes in in the first trimester and is vaccinated she can actually be eligible for a booster vaccine later in pregnancy," she said, but added it was premature for the agency to recommend boosters specifically for the pregnant.
A limitation of the study was it began during the early phase of vaccine rollout and did not include mothers who were vaccinated prior to pregnancy.
That could be a topic for future evaluation, the paper's authors wrote.
