Fact Check: Does Pfizer COVID Vaccine Lower Sperm Quality?

Concerns about the COVID vaccines affecting fertility have cropped up a few times over the course of the pandemic.

Much research has been conducted to reassure people that vaccines have no effect on fertility or pregnancy in women.

There have also been studies into whether vaccines affect sperm quality in men, one of which has been widely shared online recently.

Sperm cells
A stock image depicts sperm cells. There have been multiple studies into COVID vaccines and fertility. SciePro/Getty

The Claim

On June 17, a study was published in the journal Andrology titled 'COVID-19 vaccination BNT162b2 temporarily impairs semen concentration and total motile count among semen donors'.

The study was shared on Reddit, where it gained more than 17,000 upvotes within three days and around 1,500 comments. Some users expressed concern about the study's results, which appeared to show a temporary decline in sperm counts following vaccination.

The Facts

As its title suggests, the June 17 study does indeed appear to show that a decline in sperm concentration occurred some months after vaccination in a small group of men who volunteered to participate.

Specifically, the study investigated 220 sperm samples from 37 men who had had two doses of the Pfizer COVID vaccine. Sperm samples were received multiple times—once before vaccination (T0) once 15 to 45 days after vaccination (T1), once 75 to 150 days after vaccination (T2), and once more than 150 days after vaccination (T3).

In each sample, the researchers investigated factors such as semen volume, sperm concentration, sperm motility, and total motile count.

No significant change occurred between T0 and T1, but sperm concentration was found to be roughly 15.4 percent lower by T2 and total motile count was 22.1 percent lower. Volume and motility were not changed significantly. By T3, the reductions seemed to have recovered.

The authors stressed that rather than being concerning, their results "confirm previous reports regarding vaccines' overall safety and reliability despite minor short-term side effects."

The study reads: "Since misinformation about health-related subjects represents a public health threat, our findings should support vaccination programs."

However, the study is not conclusive despite its apparent findings. Dr. Ranjith Ramasamy, director of reproductive urology at the University of Miami Health System, told Newsweek that he considered the changes observed in the study to be within a normal range.

"Even though the numbers may be statistically significant, I don't think they achieve clinical significance," he said. "Maybe men who mount a large immune response to the vaccine could have an adverse but temporary impact but larger studies are needed to definitively answer the question."

Amelia Wesselink, research assistant professor of epidemiology at the Boston University School of Public Health, who has carried out studies into COVID vaccination and fertility, told Newsweek that it was good that the study collected multiple semen samples before and after vaccination, but highlighted its small sample size.

She also added the authors did not say whether they accounted for other factors that might affect semen characteristics, like stress or seasonal variation. Even COVID itself might affect sperm quality.

"We have known for a long time that fever can impair sperm development and function," she said. "So it certainly is possible that if fever is a side effect of vaccination, sperm quality could be harmed in the next couple of months. But the same is true for other things that cause fever—including COVID infection. And for COVID infection, there is evidence that damage to sperm can last beyond several months. So overall, these results, if causal, are not particularly concerning."

It is also not the only study to investigate vaccines and sperm quality. One study, due to be published in The International Journal of Gynecology & Obstetrics next month and published online in February, suggested that vaccines have no ill effects on sperm quality, based on 898 samples from 33 men. These men's sperm samples were tested once before their second Pfizer vaccine shot and once again at least 72 days after.

In fact, that study even suggested that total sperm count and total motile count increased after the second vaccine compared to before vaccination.

A June, 2021 study published in The Journal of the American Medical Association involving 45 men came to a similar conclusion, appearing to show that there were "no significant decreases in any sperm parameter" before and after two doses of either the Pfizer or Moderna vaccines, and also appeared to show an increase. The authors suggested this increase was "within normal individual variation and may be influenced by regression to the mean."

The Ruling

Fact Check - Mostly False

Mostly False.

One study does indeed appear to show that a second vaccine dose coincided with a temporary decline in sperm count that later recovered, but it is not a conclusive study and multiple earlier studies had shown the opposite to be true. More research on this topic is needed.


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