Vaccinated pregnant women can pass protective antibodies to their babies in utero and through breastmilk, studies suggest

  • Vaccinated moms pass COVID-19 antibodies to their babies in utero and in breastmilk, studies show. 
  • Vaccine-generated protection seems to be stronger than natural immunity from getting the virus.
  • The findings suggest vaccines are beneficial to mom and baby, though more research is needed.
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Pregnant people who get the COVID-19 vaccine seem to pass vaccine-generated antibodies to their babies in utero and through breastmilk, potentially offering the newborns protection from the virus when they’re most vulnerable. 

While past research has shown how moms who’ve had COVID-19 can pass protective antibodies on in utero and through breastmilk, the findings suggest getting vaccinated is even more protective, and safer. 

The results, which come from several studies that have yet to be peer-reviewed, help tip the scale in favor of vaccines in pregnancy — something researchers are just beginning to assess in clinical trials. 

The studies found antibodies in umbilical cord blood and breastmilk

In one preprint, researchers looked at 131 vaccinated women — 84 were pregnant and 31 were lactating. They tested their blood, umbilical cord blood, and breastmilk for COVID-19 antibodies after both vaccine doses, and again two to six weeks after the second one. (All women received either the Pfizer or Moderna vaccine.) 

They found pregnant people had just as robust an immune response as their non-pregnant counterparts, and that umbilical cord blood and breastmilk samples contained vaccine-generated antibodies. They also found moms who got the vaccine were better protected against COVID-19 than those who developed antibodies after being infected with the virus. 

When comparing the Moderna to the Pfizer vaccine, the study authors found Moderna’s gave moms a bigger boost of one type of antibody, and the bump from Pfizer’s vaccine was less robust. That could have to do with the differences in length of time between doses. More research is needed to understand if one vaccine is better than others in pregnancy.

In another study out of Israel, researchers looked at 20 moms and their babies who received both vaccine doses within about a month of delivery. They all had antibodies in their blood and umbilical cord blood. The more recently they’d gotten their vaccines, the stronger the immune response. 

“Getting the vaccine later in pregnancy can better guarantee antibody protection to babies via both the placenta and mothers’ breast milk,” Dr. Jessica Madden, a pediatrician and neonatologist who serves as medical director of Aeroflow Breastpumps, previously told Insider. 

Even getting a single dose of the vaccine before delivery can help, one case study showed. In it, doctors detailed how a baby born three weeks after her mom’s first dose of the Moderna vaccine had antibodies generated from the shot. 

We don’t yet have rigorous data on the COVID-19 vaccine in pregnancy 

The findings aren’t especially surprising, as other vaccines like for the flu are recommended in pregnancy to protect both mom and baby. 

But there’s still a lot to learn about how strong and long-lasting vaccine-generated protection from COVID-19 is in babies, and clinical trials are evaluating the safety and efficacy of getting the shot while pregnant, though experts believe they’re safe. 

“Based on how the [Pfizer and Moderna] COVID vaccine works, there should be very little risk to a developing baby,” Madden said. 

Harvard experts say the Johnson and Johnson vaccine, which is not made from mRNA but rather a harmless form of the common cold virus called adenovirus, should be safe in pregnancy too, though clinical trials still need to be conducted.

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