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Pregnant Or Lactating? Vaccinated People Might Be Passing On COVID Immunity To Their Babies

A syringe filled with the Moderna COVID-19 vaccine. (Jesse Costa/WBUR)
A syringe filled with the Moderna COVID-19 vaccine. (Jesse Costa/WBUR)

Although pregnant and lactating people were left out of the original clinical trials for coronavirus vaccines, new and encouraging data are now beginning to trickle in, says Dr. Andrea Edlow, a maternal fetal medicine doctor at Massachusetts General Hospital and medical professor at Harvard University.

In a study that she helped lead, researchers found that pregnant and lactating mothers who received the coronavirus vaccine developed strong antibodies and might also pass on those protective antibodies to their babies through the placenta and breast milk.

Edlow says the study came together in part because pregnant and lactating women didn’t know how the vaccine would affect them and their children. She was getting questions from her patients who wanted to get the vaccine, but were left in the dark because of the lack of data on pregnant people.

“We take care of these women all the time, and they have questions about, ‘Well, if this wasn’t studied in people like me, do we know that it works? Is it safe?' So, the [study] was motivated by pragmatic, real life concerns that our patients have,” Edlow says. “Once the vaccines became available and pregnant and lactating women were making the choice to get them, we said, ‘Well of course, we need to study this.’”

The study, which was published this month on medrXiv.com, followed 131 women. Eighty-four of the participants were pregnant, 31 were lactating, and the rest were non-pregnant and non-lactating women between the ages of 18 and 45.

First, Edlow and her colleagues measured the level of antibodies in the participants before and after they received the vaccine and monitored them for any side effects. The goal was to answer the most basic question of whether the vaccines work in pregnant people.

Overall, Edlow says, the response of pregnant and lactating people to the vaccine was pretty much identical to the response of non-pregnant participants in the trial. They all experienced same levels of side effects and created similar amounts of antibodies that can neutralize and destroy the coronavirus.

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“That was one really great point – it works. The vaccine works really well in pregnant women,” Edlow says.

Not only did Edlow discover high levels of protective antibodies in the women, but when 10 of the participants gave birth, the researchers were able to detect the same antibodies in all 10 of the babies’ umbilical cord blood. In particular, Edlow detected high levels of a flavor of antibody called an IgG antibody, which is associated with blood and tends to be more durable and long-lasting than other antibodies.

“There was one participant who only received one dose of a COVID vaccine [at the time of giving birth], and those antibody levels were lower in the umbilical cord blood,” Edlow says. “It seems like completing the two shots for many reasons, especially for the person’s health and safety but also to give higher doses of antibodies to the neonate, makes sense.”

People who have already given birth but were lactating when they received the vaccine are also likely transferring antibodies to their children through breast milk, Edlow adds. How exactly dousing the child’s mouth and intestinal tract with antibody-laden breast milk protects them is an area of ongoing research.

“One thing is they interact with the microbiome, the gut bacteria that are present, and can shape the baby’s immunity that way,” she says. “But we know that breastfeeding does give protection to babies and is probably complementary to the immune protection that babies receive through the umbilical cord.”

In particular, the scientists found that the breast milk contained the same IgG antibodies found in the umbilical cord blood and another type of antibody called IgA, typically associated with mucus membranes like the linings of the lungs, throat, mouth and nose. So, Edlow says, it’s also possible the antibodies stand guard on the surface of the baby’s membranes and prevent the virus from attacking that way.

“I have a friend who is currently breastfeeding. We talked about it, and I remember telling her she should get vaccinated and my hope was that she would be able to transfer antibodies to her baby,” says Dr. Sabrina Assoumou, an infectious disease physician at Boston Medical Center who did not work on the study. “So, I bookmarked this study so that I could say, ‘See! Get vaccinated! You’re helping your little daughter.’”

While the study is a preprint and has not been formally peer-reviewed, Assoumou says she’s confident in the results for several reasons. First, there’s a pile of work showing that other vaccines allow antibodies to transfer through the placenta and breast milk.

“Biologically, it makes sense. We’ve seen it in other diseases. That’s why we vaccinate the mom [during pregnancy], to protect the baby from like pertussis, [diphtheria, tetanus] and influenza,” she says. “I’m always nervous about commenting on pre-prints, but this one, the science made sense, and I knew it was from a good group.”

It’s not clear how long these antibodies last in the newborn, however. So, mothers who have been vaccinated for COVID-19 should still plan to get their children vaccinated after they’re born, Edlow says.

And until the study is formally peer-reviewed, Edlow says the results probably shouldn’t be used to inform clinical decisions just yet. But that’s also why it’s important for pregnant and lactating people to be included in clinical trials in the first place, she adds.

“They are often some of the most vulnerable individuals, especially to respiratory pathogens [like the coronavirus],” she says. “[We should] protect pregnant women and lactating women through research, not protect them from research. Why not study this group, and why not let those individuals make the choice whether or not they think it’s too risky to participate?”

This article was originally published on March 19, 2021.

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Angus Chen Twitter Reporter, CommonHealth
Angus Chen is a reporter for WBUR's CommonHealth.

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