Vaccinating pregnant women against the coronavirus can protect the newborn infants and prevent COVID-19 hospitalizations, especially if the expecting mothers get the shots later in their pregnancy, a U.S. government study suggested.

The study is the first to show potential benefits to infants born to people who received two doses of Pfizer or Moderna vaccines during pregnancy, Centers for Disease Control and Prevention (CDC) researchers said during a briefing.

It was already known that antibodies developed by COVID-19 vaccines transfer to the fetus through the umbilical cord. How that might affect infants after birth was uncertain.

"Until this study, we have not yet had data to demonstrate whether these antibodies might provide protection for the baby against COVID-19," said Dr. Dana Meaney-Delman, an obstetrician and CDC researcher.

Infants in the study were treated at 20 hospitals in 17 states from July 2021 through mid-January, during surges involving the delta and omicron variants.

The researchers didn’t examine infection rates in infants. Instead, they looked at data on 176 children under 6 months who were hospitalized with COVID-19 and 203 in the hospital for some other condition. They also looked at the vaccination status of all the babies' mothers.

Vaccination rates were much lower among mothers of the COVID-19-infected infants than among those whose infants were hospitalized with something else – 16% compared with 32%.

The results offer yet another reason for pregnant people to get vaccinated, the researchers said.

About two-thirds of pregnant people in the United States are fully vaccinated; most got the shots before pregnancy, CDC data show.

Other shots, including vaccines for flu and whooping cough, given in pregnancy are known to protect mothers and infants.

The study provides "another important piece of the puzzle," said Dr. Denise Jamieson, OB-GYN chair at Emory University, who called it important news for babies who are too young to receive COVID-19 vaccinations. While shots are being studied for older infants and toddlers, none are on the horizon for infants younger than 6 months.

"It’s not surprising, but very reassuring,’" Jamieson said.