Researchers of a recent study looking at whether the authorized COVID-19 vaccines harm male fertility were deluged with hundreds of emails from freaked-out men and their worried partners leading up to publication. Now, the findings from 45 vaccinated men are in: none showed any significant signs of lower sperm counts after getting their shots.

It’s still possible that men who experience post-vaccination side effects may suffer from lower sperm counts for a few weeks, just as they might after a viral infection. But there’s no reason to worry about significant adverse impacts on male fertility, said study co-author Ranjith Ramasamy, MD, of the University of Miami Health System, in an interview with MedPage Today. “People should not be concerned. The vaccines are very safe.”

Ramasamy, who said he himself received around 500 emails, added that the real threat to male sexual health is COVID-19 itself. The virus has been linked to lower sperm production and higher rates of erectile dysfunction.

For the study, which appears as a research letter in JAMA, Ramasamy and colleagues tracked 45 men (ages 18-50, median age 28) who’d been vaccinated with the Moderna (53%) or Pfizer-BioNTech (47%) mRNA vaccines. The study population came from South Florida, and most of the men were Latino.

The study found there was no significant decline in the men’s sperm counts at about 70 days after the final vaccine shot. “Some of the guys’ sperm counts actually increased,” Ramasamy said, although it’s not known if the vaccines are responsible for this.

According to the researchers, “the limitations of the study include the small number of men enrolled; limited generalizability beyond young, healthy men; short follow-up; and lack of a control group. In addition, while semen analysis is the foundation of male fertility evaluation, it is an imperfect predictor of fertility potential.”

Still, “even though the 45 number is small, we’re confident that we can generalize this to the rest of the population,” Ramasamy noted. “We’re pretty confident” that the Johnson & Johnson and not-yet-authorized Novavax vaccines won’t affect sperm counts either, he added.

The study authors aren’t the only ones who’ve heard from patients experiencing agita about possible vaccine-fertility links in men. “Some men even delayed getting vaccinated due to this concern as they were trying for conception,” said Parviz K. Kavoussi, MD, a reproductive urologist in Austin, Texas. “Upon questioning, the majority of men cited social media such as Facebook as their sources for information,” he told MedPage Today.

There is also widespread concern about the possible impact of the vaccines on fertility in women. The CDC has said there’s no evidence of adverse effects.

Bradley Anawalt, MD, chief of medicine at the University of Washington Medical Center in Seattle, said the study findings are good news. “In general, potential adverse effects of drugs and vaccines on reproductive function are not carefully investigated,” he told MedPage Today. “It is great to have further confirmation that the available COVID vaccines are safe and that the benefits far outweigh the risks of very rare side effects.”

But what about the risk of temporarily lower sperm counts from vaccine side effects? Ramasamy said the study didn’t turn up any sign of a problem on this front. However, Anawalt noted that “any systemic illness can transiently decrease sperm production until the illness resolves. Because it takes about 3 months for sperm to be produced and fully mature, the decrease in sperm counts occurs months after the systemic illness has resolved.”

“The common side effects of COVID vaccinations — muscle pain at the site of injection, a flu-like syndrome with muscle aches and joint aches — usually resolve after a few days,” he added. “Men are unlikely to experience significant decreased sperm counts from these short-term side effects. There are reports of people having more severe side effects — fever, severe muscle pains and joint pain — that persist for more than a few days. Men who experience a more severe reaction might have a short-term decline in sperm counts that occurs 3 to 4 months after the vaccination.”

The study authors earlier discovered that the COVID-19 virus particles remain in the penis and testes 7 to 9 months after infection, although it doesn’t appear to enter sperm in patients who recovered, Ramasamy said. The researchers have linked particles in the penis to erectile dysfunction in COVID-19 survivors.

As for sperm count, “it plummets between 3 to 6 months after the infection, and then it recovers,” he explained.

Kavoussi noted that “there are some data indicating that some men who get infected with COVID-19 may develop orchitis, which can lead to possible diminishment of testicular function. This does not mean that all men that get infected with the virus will end up infertile, but there is evidence that it may have an adverse impact on testicular function in some men.”

Anawalt offered this advice: “Get vaccinated. Good for your health. Good for your sex life.”