COVID-19 vaccines by Pfizer and Moderna do not harm male fertility, suggests a study which found the levels of sperm in participants remained at healthy levels after they got two doses of the mRNA preventive.
The study, published on Thursday in the journal JAMA, recruited 45 healthy male volunteers aged 18 to 50 years scheduled for mRNA COVID-19 vaccination by Pfizer-BioNTech and Moderna.
The participants were pre-screened to ensure they had no underlying fertility issues. Those with COVID-19 symptoms or a positive test result within 90 days were excluded.
The men provided a semen sample after two to seven days of abstinence, prior to receiving the first vaccine dose and approximately 70 days after the second shot.
Semen analyses were performed by trained andrologists as per World Health Organization guidelines and included semen volume, sperm concentration, sperm motility, and total motile sperm count (TMSC).
"One of the reasons for vaccine hesitancy is the potential negative effect on fertility," the authors of the study from the University of Miami in the US noted.
"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," they said.
In the study of sperm parameters before and after two doses of a COVID-19 mRNA vaccine, there were no significant decreases in any sperm parameter among this small cohort of healthy men, the researchers found.
Sperm concentration and total motile sperm count at the beginning of the study were 26 million/milliliter (mL) and 36 million, respectively.
After the second vaccine dose, the median sperm concentration significantly increased to 30 million/mL and the median TMSC to 44 million.
Semen volume and sperm motility also significantly increased, the researchers said.
Because the vaccines contain mRNA and not the live virus, it is unlikely that the vaccine would affect sperm parameters, they said.
The limitations of the study include the small number of men enrolled, short follow-up, and the lack of a control group.
The researchers also noted that while semen analysis is the foundation of male fertility evaluation, it is an imperfect predictor of fertility potential.
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