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

Women who received mRNA vaccines against the COVID-19 virus no longer produced an antibody theorized to reduce fertility, Yale School of Medicine researchers report in a new study.

In addition, the research team found that pregnant mice injected with mRNA vaccines had 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 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 suggests that vaccines may reduce fertility by increasing the production of the antibody against syncytin-1. According to the unproven theory, elevated levels of the antibody may interfere with placental development and prevent pregnancy. But the Iwasaki team’s study found that blood samples from 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 inactivated COVID virus vaccines.

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

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

Unvaccinated pregnant women are at greater risk of serious consequences of COVID-19 infections, including hospitalization and intensive care stays than unvaccinated pregnant women, and are at greater risk of delivering a premature or stillborn baby. Iwasaki said.

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