NICHD has delivered rigorous scientific evidence to enhance understanding of the effects of COVID-19 vaccines. Giving people more information about what to expect after vaccination can aid decision-making and potentially reduce vaccine hesitancy.
For example, an NICHD-funded study of more than 2,000 couples found that COVID-19 vaccination did not affect the chances of conception. The study showed no major differences in conception rates per menstrual cycle between unvaccinated couples and couples in which at least one partner had received at least one COVID-19 vaccine dose. The investigators did observe a short-term decline in male fertility among couples in which the male partner had tested positive for SARS-CoV-2 infection within 60 days of a given menstrual cycle. These findings suggest that SARS-CoV-2 infection, but not COVID-19 vaccination, may temporarily reduce male fertility. The results may provide reassurance for couples seeking pregnancy and aid physicians who counsel patients hoping to conceive.
Early in the pandemic, NICHD-supported research helped establish that COVID-19 vaccination during pregnancy was safe and effective. The Centers for Disease Control and Prevention now recommends COVID-19 vaccination for all people 6 months of age and older, including pregnant people. This year, a small NICHD-funded study indicated that COVID-19 vaccination during pregnancy may also help protect infants during the first 6 months of life. Compared to infants born to mothers who had COVID-19 during pregnancy, those born to vaccinated mothers were much more likely to have antibodies against SARS-CoV-2, providing another incentive for getting the vaccine.
Another small study, funded as part of the NICHD-led Predicting Viral-Associated Inflammatory Disease Severity in Children with Laboratory Diagnostics and Artificial Intelligence (PreVAIL kIds) initiative, suggested that COVID-19 vaccination is safe for children who have had multisystem inflammatory syndrome in children (MIS-C). MIS-C—a serious inflammation of the heart, lungs, kidneys, brain, skin, eyes, gastrointestinal organs, or other body parts—occurs in a small proportion of children about 4 to 6 weeks after having or being exposed to COVID-19. The condition is not well understood, and concerns were raised that administering COVID-19 vaccines to those who had MIS-C could trigger severe inflammation or a return of MIS-C. The results suggest that vaccinating children who have had MIS-C against SARS-CoV-2 could lower their risk for developing COVID-19 again, without increasing their risk for re-occurrence of MIS-C or serious inflammation.
NICHD also worked quickly to address anecdotal reports of menstrual changes following COVID-19 vaccination, by awarding a total of $1.67 million to five institutions. A large international study funded through this initiative linked COVID-19 vaccination with an average increase in menstrual cycle length of less than one day, confirming the findings of the researchers’ previous NICHD-supported U.S. study. For most study participants, the increase resolved in the menstrual cycle immediately following vaccination. The findings suggest that changes in menstrual cycle length after vaccination are minor and temporary.