Pregnant mothers who get COVID-19 vaccines are also protecting their babies

A mother lovingly hugging her baby
When mothers were vaccinated during pregnancy, the chances their baby would be hospitalized with severe COVID-19 fell an estimated 61 percent. (Images: Adobe Stock/Illustration: Patrick Bibbins, Boston Children’s Hospital)

Recent studies have shown that COVID-19 vaccination is safe for expectant mothers and can protect them against infection, severe illness, and death from COVID-19. We also know that mothers vaccinated during pregnancy pass coronavirus antibodies to their babies. The latest research — drawing on 20 children’s hospitals in 17 states — now confirms that vaccinating pregnant mothers protects their babies from severe COVID-19.

The ongoing Overcoming COVID-19 study, a national study run through Boston Children’s, identified 176 babies who were hospitalized because of COVID-19 and 203 babies who tested negative for COVID-19 and were hospitalized for other reasons. All the infants were under 6 months of age and were hospitalized between July 2021 to January 2022.

The research team then interviewed the infants’ families and checked vaccine registry records to determine the mothers’ vaccination status. They considered mothers to have been vaccinated if they had received two doses of the Moderna or Pfizer-BioNTech vaccine, with at least one of the doses given during pregnancy.

Overall, the study estimated that vaccination of pregnant mothers reduced the chances that their baby would be hospitalized with severe COVID-19 by 61 percent. The team also found that:

  • 84 percent of the babies hospitalized with COVID-19 were born to mothers who hadn’t been vaccinated.
  • 88 percent of babies admitted to the intensive care unit (ICU) with COVID-19 were born to unvaccinated mothers.

To learn more, we sat down with Dr. Adrienne Randolph, a critical care physician at Boston Children’s. Dr. Randolph directs Overcoming COVID-19 and co-led the current study with researchers at the U.S. Centers for Disease Control and Prevention (CDC), which funded the study.

What is the main takeaway from this study?

Infants are among the groups at highest risk for complications from COVID-19. In this study, we showed that completion of COVID-19 vaccination during pregnancy was associated with a reduced risk for COVID-19 hospitalization among infants. We also showed that protection was higher when their mothers were vaccinated later in pregnancy. Not only does vaccination protect mothers, it also helps to keep the baby safe from getting COVID-19.

How sick were the babies who had COVID-19?

Many of them were severely ill. Of the 176 babies hospitalized with COVID-19, 43 (24 percent) were admitted to the ICU, and 25 babies (15 percent) needed life support during their hospital stay. One of these 25 infants passed away.

How did the timing of COVID-19 vaccination during pregnancy affect protection?

We compared infants of mothers who completed their second vaccine dose during the first 20 weeks of pregnancy versus the last 20 weeks (up to 14 days before birth). We need to study this more in a larger sample of infants, but it appeared that vaccination later in pregnancy better protected the baby. We estimated it was 80 percent effective as compared with 61 percent for the group as a whole.

But it’s important to remember that vaccination protects the mother, too. The CDC, the American College of Obstetricians and Gynecologists, and the Society for Maternal-Fetal Medicine recommend COVID-19 vaccination at any point in pregnancy. A healthy parent is important for a healthy baby.

What if I was vaccinated before pregnancy?

When we started our investigation, mothers were just starting to get vaccinated, so we didn’t have a large enough sample size to look at this. We are now doing so in a larger study.

Did the study say anything about COVID-19 booster shots during pregnancy?

Our study started in July 2021, and booster shots only started to be given in late fall 2021. So we did not have enough mothers receiving boosters to answer this question, but we hope to do so when we have more data.

Did the study look at the effects of breastfeeding?

Again, we will need to study a larger group of infants to get a definitive answer. In our relatively small sample, the babies without COVID-19 were more likely to be breastfed: 65 percent were breastfed, as compared with 55 percent of babies with COVID-19. We are collecting more data to better estimate the potential protectiveness of breastfeeding. But we do know that mothers can transmit antibodies to the coronavirus to their babies through their breastmilk.

Is this study continuing?

We are continuing this investigation and now have doubled the number of enrolled infants hospitalized with COVID-19. We are planning to reanalyze the data soon. The larger sample size will give us more information on timing of vaccination during pregnancy and protection of babies from COVID-19.

Learn more about COVID-19 research at Boston Children’s Hospital

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