Getting vaccinated against COVID-19 does not reduce the chances of successfully becoming pregnant for couples who are trying to conceive, suggests data from a study by researchers at Boston University. However, men in the study who tested positive for the virus appeared to have at least "a short-term decline in fertility." 

The findings were published this week as a manuscript in the American Journal of Epidemiology. They add to a growing body of evidence supporting use of the vaccines to both protect pregnant women and reduce risk to their babies. The Centers for Disease Control and Prevention, as well as outside medical groups, have urged all people trying to become pregnant to be vaccinated. 

Researchers drew on data from people enrolled in Boston University's years-long Pregnancy Study Online.

"The findings provide reassurance that vaccination for couples seeking pregnancy does not appear to impair fertility," Dr. Diana Bianchi, head of the arm of the National Institutes of Health that funded the study, said in a release announcing the results. 

The study's authors say they surveyed participants — adult women up to 45 years old who are trying to conceive without the use of fertility treatments — and many of their partners every eight weeks for a year. 

A statistical analysis of data collected from the participants found "no meaningful association" between couples who reported COVID-19 vaccination and the likelihood they were able to conceive, compared to unvaccinated participants. 

That also held true across a variety of other factors, the researchers said, including vaccination brand and different times of the year.

However, male partners who reported they tested positive for COVID-19 appeared to be associated with "a transient reduction" in the likelihood of conception within 60 days.

"These findings indicate that male SARS-CoV-2 infection may be associated with a short-term decline in fertility," they said. 

Some studies have found at least a temporary drop in the body's production of sperm following a symptomatic infection from SARS-CoV-2, the virus that causes COVID-19. That could be as a result of days-long fevers caused by COVID-19, longer than the single day of mild side effects seen after vaccination. 

The Boston University researchers plan to continue following participants to monitor for any potential "long-term associations" between vaccination and "fecundability" — the likelihood that couples are able to conceive within a single menstrual cycle. "However," they add, "it is unlikely that adverse effects on fertility could arise many months after vaccination." 

Public health officials have for months urged couples to get vaccinated, citing significant risks posed by COVID-19 to people who catch the virus while pregnant.

The virus could also increase risks of stillbirth, scientists have warned. One recent study by NIH scientists, published in Nature, also spotted inflammation in children who were carried by infected mothers that might "lead to long-term morbidities."

"We know that pregnant people with COVID-19 can become very sick. Some will die, and many will experience pregnancy and neonatal complications. We know that, because of COVID, some children will grow up without their mothers," the CDC's Dr. Dana Meaney-Delman told the agency's outside vaccine advisers last year.

Long a concern for health authorities, rates of COVID-19 vaccination among people who are pregnant or trying to become pregnant have improved in recent months. CDC survey data suggests their vaccination rates now track more closely to those of younger adults overall.

However, concerns over fertility and vaccination persist, pushed in part by misinformation on social media. A survey published in November by the Kaiser Family Foundation found nearly 3 in 10 U.S. adults believe or were unsure about whether vaccines had been shown to cause infertility.

"We know that COVID-19 vaccines are safe and effective. If you are pregnant, postpartum, breastfeeding, trying to get pregnant now, or might become pregnant in the future, please get vaccinated," said Meaney-Delman.