Pfizer's COVID-19 vaccine leads to lower levels of semen, according to a new study.
Researchers analyzed 220 samples of semen from three sperm banks in Israel, drawn from men who received two doses of the vaccine. The semen collection was scheduled seven days after receipt of the second dose.
The researchers, led by Dr. Itai Gat with the Sperm Bank and Andrology Unit at the Shamir Medical Center and Tel Aviv University's Sackler Medical School, found that there was a decrease in sperm concentration between 75 and 120 days post-vaccination.
The decrease led to a reduction in the motile count, or the number of sperm.
Followup testing completed over 150 days after vaccination revealed "overall recovery," with semen volume and sperm motility bouncing back, the researchers said. However, the levels outlined in the study were still lower than before vaccination.
The latter measurements were "not statistically significant" compared to the first ones, even though they were still lower, Gat told The Epoch Times in an email.
Pfizer did not respond to a request for comment.
Gat said that a major strength of the study was the relatively long-term followup.
"Overall we demonstrate long term safety of the vaccination regarding semen analysis among sperm donors. The temporary decline we found is similar to already known side effects of short febrile illness (ex. flu), followed by later recovery," he said in an email. "It seems that the immune response after vaccination is similar as in cases of common infections which results with short term impairment of sperm production."
Previous research has indicated that getting sick with COVID-19 causes a change in the composition of semen, and that some illnesses can lead to sperm production being impaired.
Men should only be concerned by the new research as much as they worry about similar issues arising after other infections, Gat said.
"Obviously, most men are not aware of the short decline in their sperm counts after viral infection," he said.
However, researchers acknowledge that the long-term impacts of the shots remain unknown, and won't be known until longer-term studies are conducted.
Gat wants to conduct further research on men who were vaccinated but described his team as lucky to have a large group of donors who were vaccinated during a short period of time.
"When it comes to next doses, I expect timing diversity between donors, which will make further studies much more complicated," he said.