When moms get vaccinated during pregnancy, babies get protection too, study shows

Getting vaccinated against COVID-19 during pregnancy may also help protect babies after they're born, according to new research published by the Centers for Disease Control and Prevention.

Babies whose mothers received two shots of either the Pfizer or Moderna vaccines during pregnancy had a 61% lower risk of being hospitalized with COVID in their first six months of life, the study found.

"The bottom line is that maternal vaccination is a really important way to help protect these young infants," said Dr. Dana Meaney-Delman, chief of the CDC's Infant Outcome Monitoring, Research and Prevention branch. She notes that is particularly important because there's no vaccine authorized for babies under 6 months old.

The researchers looked at data on 379 infants hospitalized for various reasons, including COVID, across 17 states from July 1, 2021 through Jan. 17. The vast majority – 84% – of the babies hospitalized with COVID were born to mothers who had not been vaccinated.

Previous studies have shown that people vaccinated against COVID during pregnancy can transfer protective antibodies to their unborn fetus. That includes a small study published in JAMA last week, which found that 98% of babies whose mothers were vaccinated during pregnancy still had detectable levels of protective antibodies two months after birth. And 57% of the infants still had detectable antibody levels six months after birth.

Now, the new study from the CDC offers real-world proof that these antibodies from mothers who were vaccinated while pregnant translate into protection for infants, says Dr. Andrea Edlow, a maternal fetal medicine physician at Massachusetts General Hospital in Boston and associate professor of obstetrics and gynecology at Harvard Medical School, who was not involved in the CDC study.

"I think it's a very important study because it shows real-world efficacy, and we know that antibody titers are a correlate of protection, we always are saying antibody levels are correlates of protection. But here they actually showed the correlation that it is protective. So I think that's an incredibly important message from this study," Edlow says.

The CDC study didn't include people who received the Johnson & Johnson vaccine, nor did it look at the effects of maternal booster shots on infants. Study co-author Dr. Manish Patel says the researchers aim to look at the effect of boosters in the future.

"I think it's fair to say from all of the evidence on boosters increasing protection and antibody levels, that we should see higher protection, definitely not lower protection with boosters," Patel says.

In the new CDC study, the protection against COVID hospitalization appeared stronger for babies whose mothers got vaccinated after 21 weeks of pregnancy. That jibes with earlier research that has found that the transfer of antibodies from mother to child is at its peak during the second and third trimesters of pregnancy, says Edlow, who co-authored the JAMA study.

But Edlow warns that expectant mothers should in no way delay getting vaccinated in order to optimize protection for their fetus. She notes that people who get COVID while pregnant face much higher risks of severe outcomes – not just from COVID itself but other serious hypertensive complications of pregnancy, such as preeclampsia and postpartum hemorrhaging.

"I think it's a great secondary benefit that the maternal antibodies can cross the placenta and can protect the neonatal infant," Edlow says. "But that is not the main point of COVID vaccination during at this phase in the pandemic. It's really to protect the mother."

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