Pfizer and Moderna vaccines do no harm to male fertility, says study

The Pfizer and Moderna COVID vaccines pose no threat to male fertility, a finding experts hope will prompt more men to get vaccinated.

Researchers noted that the original clinical trials of the two mRNA vaccines didn't assess how they might affect fertility.

"Vaccine hesitancy is a barrier to ending the COVID-19 pandemic, and we believe some of that hesitancy is due to public opinion about whether the vaccine might negatively affect fertility," said senior study author Dr. Ranjith Ramasamy, director of the Reproductive Urology Program at the University of Miami's Miller School of Medicine.

"We were the first to demonstrate that the COVID virus, itself, can affect male fertility and be a potential cause for erectile dysfunction," he said in a university news release. "We are now the first to examine if there is any impact of the COVID vaccine on male fertility potential, which we did not find."

The study included 45 healthy men between the ages of 18 and 35, who had no fertility problems. They provided a semen sample before receiving the first dose of either the Pfizer or Moderna vaccine and another sample about 70 days after their second dose.

"This is the full life cycle of sperm and 70 days is sufficient time to see if the vaccine impacts semen parameters," said study first author Daniel Gonzalez, a medical student at the Miller School.

He said measurements of semen volume, sperm concentration and moving sperm found no declines from initial levels.

Ramasamy said the findings—which were published online June 17 in the Journal of the American Medical Association—could go a long way toward reducing vaccine hesitancy.

The study did not assess the single-dose Johnson & Johnson COVID-19 vaccine.