The vaccine contains mRNA, not the live virus, so it is unlikely to affect sperm.
Study of 45 healthy men showed no significant decreases in sperm parameters after two mRNA vaccine doses, with some metrics actually increasing. Researchers attribute increases to normal fluctuations and increased abstinence time rather than vaccine effects, noting the study had limitations and lacked a control group.
- Study of 45 healthy men, ages 18-50, conducted December 2020 to April 2021
- Average sperm count rose from 26 million to 30 million cells per milliliter after vaccination
- Only 56% of men surveyed said they would accept an mRNA vaccine despite high efficacy
- COVID-19 itself causes inflammation and reduced sperm quality, separate research found
University of Miami research published in JAMA found mRNA COVID vaccines do not alter sperm quality or quantity, countering widespread misinformation that deterred vaccine uptake among men.
Researchers at the University of Miami set out to answer a question that had taken root in social media and was keeping men away from vaccination: Does the COVID-19 vaccine damage sperm? The answer, published in JAMA, was no. The mRNA vaccines from Pfizer-BioNTech and Moderna did not alter sperm quality or quantity in any meaningful way.
The study emerged from real concern. Only 56 percent of men surveyed said they would accept one of these vaccines, despite their proven effectiveness. The misinformation was working. So between December 2020 and April 2021, the Miami team designed a careful test. They recruited 45 healthy men between 18 and 50 years old who had no history of infertility problems. Anyone showing COVID symptoms or testing positive in the previous 90 days was excluded. Each participant provided a semen sample after two to seven days without sex, then again roughly 70 days after their second vaccine dose. The researchers measured semen volume, sperm concentration, sperm motility, and total sperm count.
What they found was reassuring but modest. Average sperm count actually rose slightly, from 26 million cells per milliliter to 30 million after the second dose. Semen volume and sperm motility both increased as well. The largest individual increase was around 90 percent; the largest decrease was 20 percent. But the researchers were careful not to claim victory for the vaccine. These swings fell within the normal range of fluctuation for sperm counts. The increase might have come from something simpler: the men had abstained longer before providing the second sample, which naturally boosts numbers. "The vaccine contains mRNA, not the live virus," the authors explained, "so it is unlikely to affect sperm parameters."
The study had real limits. It was small, the follow-up was short, and there was no control group of unvaccinated men to compare against. Sperm analysis itself, the researchers noted, is an imperfect measure of actual fertility potential. Still, the timeline did span the full life cycle of sperm production, giving the findings some weight.
The larger context made the study matter more. A separate investigation published earlier that year in the Society for Reproduction and Fertility found that COVID-19 itself posed a threat to male fertility. When researchers compared semen from healthy men to those who had recovered from the disease, they found inflammation and oxidative stress in the infected group, along with measurable changes in sperm concentration and movement. The virus, not the vaccine, was the danger. This finding reframed the whole question: vaccination was not a risk to reproductive health—it was protection for it.
Citas Notables
The vaccine contains mRNA, not the live virus, so it is unlikely to affect sperm parameters.— University of Miami researchers, published in JAMA
The increases may be due to normal fluctuations in sperm count and increased abstinence time before the second sample, not the vaccine itself.— Study authors
La Conversación del Hearth Otra perspectiva de la historia
Why did researchers feel they needed to run this study at all? Was there any biological reason to suspect the vaccine might harm sperm?
Not really. The vaccine is just genetic instructions—mRNA—not a live virus. But the rumor spread anyway, and it was keeping men from getting vaccinated. When only half of men say they'll take a vaccine that works, you have a problem worth investigating.
So they tested 45 men. That's not a huge number. How confident can we be in the results?
Fair question. The researchers themselves said the study was limited. No control group, short follow-up period. But what matters is that they found nothing alarming. If the vaccine were harming sperm, you'd expect to see it even in a small sample.
The sperm counts actually went up. Doesn't that suggest the vaccine helped?
That's what it looks like on the surface. But the researchers were honest about it. The increases fell within normal variation. Men also waited longer between the first and second sample, which alone can boost numbers. They weren't claiming the vaccine improved fertility.
What about the virus itself? Did the study address that?
Not directly, but other research did. COVID-19 actually damages sperm production—causes inflammation, oxidative stress, changes in concentration and movement. So the real threat to male fertility wasn't the vaccine. It was the disease.
So vaccination protects fertility rather than threatens it.
Exactly. That's the thing the misinformation got backwards.