A new study shows that Covid-19 vaccines don't impair fertility in men or women — but a Covid infection could potentially affect a man's fertility for up to 60 days.
Research funded by the National Institutes of Health and published on Thursday in the American Journal of Epidemiology tracked data from more than 2,100 women and some of their partners in the U.S. and Canada for roughly a year, ending in November 2021.
It found that getting vaccinated against Covid had no discernable effects on fertility rates in either men or women, adding to a growing body of evidence regarding the safety of Covid vaccines.
The study also found that men who tested positive for Covid within 60 days of their partner's menstrual cycle were 18% less likely to conceive during that cycle, compared with men who had not tested positive.
"There's not necessarily any harm in trying to conceive shortly after having Covid, but it may just take a bit longer," Amelia Wesselink, a study co-author and research assistant professor of epidemiology at the Boston University School of Public Health, tells CNBC Make it.
Wesselink says the findings showed no long-term effects from Covid infections on male fertility, or any effects on female fertility.
More research is needed to determine why male fertility drops after Covid infections. However, it's worth noting that fever is a common Covid symptom — and fevers are known to temporarily reduce sperm count and motility, according to the NIH.
Dr. Boback Berookhim, director of male fertility and microsurgery at Lenox Hill Hospital in New York City, says men who had symptomatic Covid with high fevers can potentially experience a temporary decline in sperm count that's likely to rebound after a couple months.
"Sperm production generally requires normal body temperatures," he says.
Dr. Adi Katz, Lenox Hill's director of gynecology, says inflammation caused by an infection may also play a role in reducing sperm quality. Multiple studies have now shown that Covid infections can affect male fertility, mostly in people who fall moderately to severely ill, she adds.
Researchers in the NIH-funded study noted that the short-term decline in male fertility could potentially be avoided by getting vaccinated against Covid. Wesselink says she hopes the study results can help couples make informed decisions about Covid vaccinations, and provide reassurance that getting vaccinated will not harm their chances of conceiving.
To conduct the study, researchers collected data from more than 2,100 women, ages 21 to 45, in the U.S. and Canada from December 2020 through November 2021. Subjects were asked to complete health questionnaires online every eight weeks until they became pregnant, or for a year if they did not.
Participants were also asked questions about their male partners, and given the option to invite their partners to complete similar questionnaires. Nearly 25% of them did so. At the time of the study, 73% of the women and 74% of the men had received at least one dose of a Covid vaccine.