COVID vaccines do not impact fertility or pregnancy outcomes, study shows

Women who received mRNA vaccines against the COVID-19 virus did not produce more of an antibody that had been theorized to reduce fertility, Yale School of Medicine researchers report in a new study.

In addition, the research team found pregnant mice injected with mRNA vaccines suffered no side effects and produced normal offspring, according to the research, published May 24 in the journal PLOS Biology.

“The findings provide further evidence that existing mRNA vaccines are safe for pregnant women and those planning to become pregnant,” said Akiko Iwasaki, Sterling Professor of Immunobiology and of Molecular, Cellular & Developmental Biology and senior author of the paper.

Alice Lu-Culligan and Sasha Tabachnikova, doctoral students in Iwasaki’s lab and co-authors of the paper, set out to address a variety of concerns about vaccines’ effects on fertility and pregnancy. One widely circulating theory posits that vaccines might reduce fertility by increasing production of the antibody against syncytin-1. According to the unproven theory, increased levels of the antibody can interfere with placental development and prevent pregnancy. But the Iwasaki team’s study found that blood samples of vaccinated and unvaccinated women showed no differences in levels of anti-syncytin-1 antibodies. And the authors found no evidence of such antibodies in people vaccinated with either mRNA COVID vaccines or with inactivated COVID virus vaccines.

To address concerns that vaccines received during pregnancy might cause birth defects, researchers injected pregnant mice with a large dose of mRNA vaccines and followed the health of the mice and fetus. Pregnant mice showed no ill health effects and their fetuses exhibited no physical defects or unusual limitations on growth. In addition, the fetuses of vaccinated pregnant mice had higher levels of circulating antibodies to the SARS-CoV-2 virus, suggesting they would be protected against this infection after birth.

The findings emphasized the importance of vaccinations for both pregnant women and those considering becoming pregnant, Iwasaki said.

“Unvaccinated pregnant women are at increased risk for severe consequences of COVID-19 infections, including hospitalization and intensive care stays than unvaccinated pregnant women, and face increased risk of delivering a preterm or stillborn infant.” Iwasaki said.