Men afraid of getting the Pfizer COVID-19 vaccine in case it affects their fertility can rest easy - a new study has found it has no negative effect on sperm count whatsoever.
In fact - and contrary to what conspiracy theorists have claimed about the mRNA-based vaccines - men in the study ended up having better-quality sperm.
"One of the reasons for vaccine hesitancy is the potential negative effect on fertility," the researchers said.
"Because reproductive toxicity was not evaluated in the clinical trials and SARS-CoV-2 has been associated with decreases in sperm parameters, we assessed sperm parameters before and after mRNA vaccine administration."
SARS-CoV-2 is the formal name of the virus which causes the disease COVID-19, which has been linked to negative impacts on sperm count and health.
Researchers at the University of Miami took two semen samples from 45 healthy men aged between 18 and 50. The first was before they had any shots, the second about two-and-a-half months after they'd been fully vaccinated.
After being fully vaccinated with either the Pfizer or Moderna vaccine, the average sperm concentration rose between 15 and 20 percent, while "motility also significantly increased" - motility being a proxy for sperm health.
"We found no changes in sperm parameters in the young healthy men that we studied who received both doses of mRNA vaccine," study author Ranjith Ramasamy of the University of Miami told CNN.
He added that the same probably goes for other vaccines that weren't tested - specifically those made by Janssen and AstraZeneca, which have had problems with rare cases of blood clots.
"We think the mechanism of how these vaccines work is all fairly similar despite different genetic material, so based on biology, we don't think there should be anything different with the other two vaccines."
The "statistically significant" increased number of sperm was likely down to "normal individual variation" and probably not the vaccine itself, the researchers concluded.
A study earlier this year found SARS-CoV-2 could hurt male fertility. It's not known if the effects are temporary or long-term yet, with the virus still new to science.