The verdict is in: Pregnant women pass COVID-fighting antibodies to their unborn children

• Pregnant women pass coronavirus antibodies to their unborn children, a spate of research suggests.
• A new study found high antibody levels in newborns whose mothers had received the Pfizer or Moderna shots.
• Studies have also shown that mothers can transfer antibodies to infants through breast milk.

New data suggests COVID-19 vaccines do more than protect mothers-to-be: Pregnant women also pass coronavirus antibodies to their unborn children.

A new study from researchers at New York University found high levels of coronavirus antibodies in the blood of newborns whose mothers had received the Pfizer or Moderna vaccine. The study looked at 36 newborns and found that all of them had antibodies when they were delivered.

Mothers who'd been vaccinated 13 weeks before giving birth seemed to pass along higher levels of antibodies than mothers who'd been vaccinated more than 20 weeks before giving birth. But the researchers said more data is needed to determine whether there's really a correlation between the timing of the vaccine and a newborn's antibody levels.

It's also not yet clear how well the newborn babies were protected from coronavirus infections, or how long that protection might last. Still, the researchers suggested coronavirus antibodies may give infants protection during the neonatal period - their first four weeks - or longer.

"If babies could be born with antibodies, it could protect them in the first several months of their lives, when they are most vulnerable," Ashley Roman, one of the study authors, said in a press release.

The team wrote that their findings "add to a growing list of important reasons why women should be advised to receive the COVID vaccine during pregnancy."

Babies can inherit antibodies from vaccines or infections

Pregnant women develop antibodies in response to a vaccine or an infection, then transfer them in two key ways. Antibodies can travel from the placenta to unborn children through the umbilical cord. Newborns can also take in these antibodies through breast milk. That's true for antibodies from other vaccines, too, like the flu shot.

A January study found that pregnant women who'd had COVID-19 transferred coronavirus antibodies across the placenta to their unborn children. Of the 83 women in that study who had antibodies at the time they gave birth, 87% passed them to their children. A similar study looked at 88 pregnant women who'd had prior coronavirus infections and found that around 78% of their newborns inherited antibodies.

But ultimately, newborns may get the best protection from vaccinated mothers: Several studies have found that pregnant women develop higher antibody levels if they're vaccinated than if they previously had COVID-19.

Protection from vaccines also develops fairly quickly. An August study found that pregnant women developed antibodies from either the Pfizer or Moderna shots as early as five days after their first dose, then transferred those antibodies to their newborn babies as early as 16 days after the first dose.

The benefits of COVID-19 shots outweigh the risks for pregnant women and their babies

US regulators began recommending COVID-19 vaccines for pregnant women in April.

Studies have shown that the shots are highly effective for these women: Pfizer's vaccine lowered the risk of coronavirus infections by 78% among 7,500 pregnant women in Israel, according to a July study. (Pfizer is also currently doing its own study of how its vaccine performs among pregnant women.)

The shots don't pose any serious safety risks for pregnant women, either. The Centers for Disease Control and Prevention reported last month that the Pfizer and Moderna vaccines haven't increased the risk of miscarriage among US women. And an August study from NYU found that COVID-19 vaccines didn't increase the chances of birth complications or harm to the fetus, either.

The risk of dying from COVID-19, meanwhile, is nearly twice as high for pregnant women as it is for nonpregnant women of the same age. Infants also have a higher risk of severe COVID-19 than older kids, likely because their immune systems are less developed.

And yet, as of August, just 23% of pregnant women in the US were vaccinated.