• A pre-print study in Israel found no change in sperm of men who got Pfizer's COVID-19 vaccine.
  • The study was small, but it's some of the first data we have on vaccines and male fertility.
  • There's plenty of research finding the vaccines are safe for women who are pregnant or trying to be.
  • See more stories on Insider's business page.

Pfizer-BioNTech's COVID-19 vaccine does not damage sperm, according to a small new pre-print study out of Israel.

Researchers studied sperm samples from 43 men who had received their second dose of the vaccine around a month prior.

The team at the Hebrew University of Jerusalem found no abnormalities in the volume, concentration, or motility of the men's sperm. 

Though the study was small, and the results have yet to be peer-reviewed, the researchers believe their findings are a ringing endorsement for young men to get vaccinated, pointing to research that suggests coronavirus infection could impact male fertility.

"These preliminary results are reassuring to the young male population undergoing vaccination worldwide," they wrote Monday on the website medRxiv, where researchers post pre-print studies. "Couples desiring to conceive should vaccinate, as vaccination does not affect sperm."

Does COVID-19 infection affect male fertility?

A controversial paper published in the journal Reproduction in January caused a stir among scientists, suggesting there is evidence that COVID-19 impacts male fertility.

While that is plausible, Dr. Channa Jayasena, a consultant in reproductive endocrinology and andrology at Imperial College London, told CNN, the study lacked detail and convincing data.

"Being ill from any virus such as flu can temporarily drop your sperm count (sometimes to zero) for a few weeks or months. This makes it difficult to work out how much of the reductions observed in this study were specific to COVID-19 rather than just from being ill," Jayasena said.

We know the vaccines do not affect female fertility

how mRNA vaccines work infographic

An infographic showing how mRNA vaccines are developed.

Shayanne Gal/Insider


Despite some fierce misinformation campaigns, experts say it is physically impossible for the virus to impact women's fertility.

The vaccines from Pfizer and Moderna use messenger RNA (mRNA) to train the body to recognize and fight the coronavirus.

As the American College of Obstetricians and Gynecologists said in an advisory notice: "These vaccines do not enter the nucleus and do not alter human DNA in vaccine recipients. As a result, mRNA vaccines cannot cause any genetic changes."

Jerica Pitts, a spokesperson for Pfizer, reiterated the point, telling the Associated Press: "It has been incorrectly suggested that COVID-19 vaccines will cause infertility because of a shared amino acid sequence in the spike protein of SARS-CoV-2 and a placental protein. The sequence, however, is too short to plausibly give rise to autoimmunity."

Experts are excited to get some data on male fertility, the virus, and the vaccine

While none of the clinical trials of the vaccines knowingly included pregnant people, there is now plenty of data to show that the vaccines are safe for women trying to conceive, people who are currently pregnant, and those who are breastfeeding.

But this Israeli study represents some of the first data on male fertility.

Speaking about the vaccines and fertility in an Insider webinar last month, Dr. Jessica Shepherd, an OB/GYN, lamented the lack of attention paid to men in this conversation.

"Most times when we think of studies, especially with something that's so new, we do focus on people who are currently pregnant and then breastfeeding moms and the recent postpartum phase," Shepherd said. "But many times we do have to consider the male factor of fertility and seeing if there's any impact on sperm."

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