Vaccinated Pregnant Women Pass COVID-19 Immunity to Their Newborns

Getting vaccinated against COVID-19 not only protects pregnant people but their babies too, more research is finding. A new study shows that pregnant women who get the vaccine pass on antibodies to their newborns.

Researchers from New York University's Grossman School of Medicine examined whether immunity transferred to the newborn after a pregnant woman received one dose of the Pfizer or Moderna vaccine starting at the time of the Food and Drug Administration’s (FDA) emergency use authorization on June 4, 2021.

“The study is very important because vaccination not only protects the mom, but it protects the baby for the first few months of life,” Jennifer L. Lighter, MD, pediatric epidemiologist and the study’s co-author, tells Verywell. 

To determine whether immunity was passed to the newborn via the vaccine, Lighter and her team looked specifically at an antibody called IgG. 

When mothers get vaccinated, IgG antibodies are passed to babies in the womb, according to Ashley S. Roman, MD, director of maternal-fetal medicine at NYU and the study’s coauthor.

“We do know, from other models, this is an antibody type that does cross the placenta very well," Roman tells Verywell. "And that’s why we looked at that very specifically."

After vaccination, Roman says that the mother mounts her immune response to the vaccine. That immune response then transfers over.

“The IgG antibody type that is built to the COVID spike protein crosses the placenta and becomes present in the fetus's blood,” Roman says. “This is what we are able to detect at birth by testing the umbilical cord blood.”

IgG was analyzed using umbilical cord blood collected from 36 deliveries.

To make sure the immunity that was passed on was specifically from the vaccine and not infection, Roman and Lighter looked at two different antibodies: positive anti-S IgG and negative anti-N IgG. Anti-N antibodies are antibodies that are built from natural infection whereas anti-S antibodies are built from both the vaccine and natural infection. 

If a mother tests positive for anti-N and anti-S, the mother had a natural infection, Roman says. If a mother tests positive for anti-S and negative for anti-N, it represents a response to the vaccine. 

“We were able to show in this study that in 36 women, all of it came from the vaccine,” Roman says. 

Should Pregnant People Get Vaccinated?

According to the Centers for Disease Control and Prevention (CDC), pregnant people are strongly encouraged to get the COVID-19 vaccine.

“CDC encourages all pregnant people or people who are thinking about becoming pregnant and those breastfeeding to get vaccinated to protect themselves from COVID-19,” Rochelle Walensky, MD, MPH, director of the CDC, said in a press release. 

The CDC reports that there have been no safety concerns for pregnant people who were vaccinated with Moderna or Pfizer and no risk for miscarriage.

They also state that there are no adverse pregnancy-related outcomes in clinical trials associated with the Johnson and Johnson COVID-19 vaccine. The vaccines do not cause infection in pregnant people and their babies.

“The vaccines are safe and effective, and it has never been more urgent to increase vaccinations as we face the highly transmissible Delta variant and see severe outcomes from COVID-19 among unvaccinated pregnant people,” Walensky said. 

The benefits of receiving a COVID-19 vaccine outweigh any known or potential risks of vaccination for pregnant people. In fact, getting COVID-19 is more dangerous.

Research shows that those who got COVID-19 during pregnancy experienced an increased risk for preeclampsia, severe infections, intensive care unit admission, preterm birth, and mortality compared to pregnant women without COVID-19.

Future Research

More research is needed to determine whether vaccination in the second half of pregnancy may confer higher levels of antibody transfer compared to vaccination earlier in the pregnancy. 

Due to the small sample of pregnant women, Roman and her team were unable to examine the optimal timing of vaccination and its impact on transfering immunity. They hope to examine this further.

According to Roman, the National Institutes of Health is currently conducting a trial, also known as MOMI-VAX, to determine the neonatal benefits of vaccination and the duration of antibodies after the baby is born.

Studies like MOMI-VAX and the one conducted by Lighter and Roman will help fuel future research.

“Lots of work still to be done," Roman says. "But this is one building block to get us there." 

But by getting vaccinated during pregnancy and even before, “women can protect themselves and their families from getting COVID,” Roman says.

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