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New Study Confirms That COVID-19 Vaccine Does Not Affect Male Fertility

Man and woman holding pregnancy test

Key Takeaways

  • The University of Miami completed a study to measure sperm parameters of participants who received a COVID-19 vaccine.
  • The study tracked the motility and concentration of sperm to see how they were impacted by the mRNA vaccine.
  • This study adds to the existing body of research that shows that the COVID-19 vaccine does not cause infertility.

In 2020, a cohort study found SARS‐CoV‐2 RNA in male semen. The study did not prove that the virus could be transmitted sexually, only that the virus was detected in the semen of people who were ill or recovering. This discovery resulted in speculation about whether COVID-19 could have effects on a fetus or on fertility.

Data is still being collected about COVID-19's impact on pregnancy and fetuses. Currently, evidence shows that pregnant people are at increased risk for severe illness. In addition, they are at risk for preterm birth and other poor pregnancy outcomes. So, concerns about the virus's affect on a pregnancy are warranted.

Pregnant people can receive the COVID-19 vaccine. Pregnant people were not included in vaccine clinical trials, but early data from safety monitoring systems has not identified any safety concerns.

More recently, there have been concerns around whether or not the COVID-19 vaccine could affect sperm quality. Research has never supported this concern, and a study completed in 2021 offers empirical evidence to quell those concerns.

Study Results

A study at the University of Miami tested the semen of 45 participants, ages 18 to 50, prior to receiving a first dose of the vaccine and again 70 days after receiving the second dose. The study found that no significant decreases in sperm parameters.

Since the vaccines contain mRNA and not the live virus, it is unlikely that the vaccine would alter sperm parameters. Interestingly, the study found a statistically significant increase in all sperm parameters. In fact, before receiving the vaccine, eight study participants had low sperm count. Of the eight, seven fell within normal sperm count range after the vaccine, and one remained low.

Researchers believe that the increased sperm parameters fell within individual normal variation and could be the result of the increased abstinence time before the second sample was taken (abstinence of three days was required prior to collecting the second sample).

Ranjith Ramasamy, MD

We were the first to demonstrate that the COVID virus, itself, can affect male fertility and be a potential cause for erectile dysfunction. We are now the first to examine if there is any impact of the COVID vaccine on male fertility potential, which we did not find.

— Ranjith Ramasamy, MD

Prior to completion, researchers explained what they expected to find. Based on how the vaccines work, they anticipated that the study would confirm that the COVID-19 vaccines do not cause male infertility.

Urology fellow and co-author Daniel Nassau, MD, explains the study. “We are going to evaluate sperm production and sperm quality for men who are thinking about fertility either at present or in the future and will receive the COVID-19 vaccine," he says. "We want to see if there is any decrease in sperm production or quality. We will look at a semen sample before they get the vaccine and then at three to six months thereafter.” 

How does the mRNA vaccine work?

Microbiologist and immunologist Andrea Love, PhD, has dedicated three podcasts to debunking vaccine myths, including one about female infertility. She explains, “The current myth suggests that the immune response to the mRNA COVID-19 vaccines causes the body to attack syncytin-1, a protein in the placenta, which could lead to infertility in women."

Love continues, "The claim states that the SARS-CoV-2 spike protein, which is what the RNA in the vaccine encodes, is so similar to the placental protein syncytin-1 that it leads to cross-reactivity. Cross-reactivity means that our immune system can’t tell the difference between the two proteins and reacts to this placental protein as well.”

She says that all proteins are made up of amino acids, and the mRNA vaccines have amino acid sequences in common in a row. “That .39% homology, or protein similarity, would never lead to a cross-reactive response. Proteins need almost complete similarity in order to be mistaken for one another by our immune system, therefore infertility could not happen.” 

Love also points to current clinical trials refuting the claim. In fact, 23 participants in the Pfizer-BioNTech vaccine clinical trial were dismissed because they became pregnant during the trial, with 12 of them being in the vaccine group.

Registries and trials in pregnant people are currently underway. BioNTech and Pfizer's phase 2/3 placebo-controlled trial will include about 4,000 pregnant adults between 24 and 34 weeks' gestation. The study is expected to conclude in July of 2022.  

What is the vaccine made of, anyway? 

According to the CDC, the Pfizer-BioNTech vaccines contains the following: mRNA, lipids ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 2 [(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 1,2-Distearoyl-sn-glycero-3- phosphocholine, and cholesterol), potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate, and sucrose.

Andrea Love, PhD

That .39% homology...would never lead to a cross-reactive response. Proteins need almost complete similarity in order to be mistaken for one another by our immune system, therefore infertility could not happen.

— Andrea Love, PhD

Love breaks these complicated ingredients down, “Despite the science terms, the mRNA COVID-19 vaccines have a quite simple formulation." They contain a sequence of:

  • RNA, which is the template for our cells to manufacture the spike protein of COVID-19, aka the piece of the virus that our immune system recognizes and responds to
  • Lipids to help transport and stabilize the RNA
  • Buffers to normalize the pH and make it compatible with the pH of our bodies
  • Sugar as a cryoprotectant, since the vaccine dosages are stored in freezer conditions.

Love asserts that while some of these ingredients may sound like scary chemicals, they're effectively harmless, and shouldn't deter you from getting the vaccine.

What This Means for You

The COVID-19 vaccine will still need extensive research, but the chances are very low that there are any negative consequences. In fact, the results of the University of Miami clinical trials confirm what scientists have presumed all along—the COVID-19 vaccine does not affect male fertility.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  5. University of Chicago Medinine. COVID-19 vaccines and pregnancy: What to know if you're pregnant, trying to conceive, or breastfeeding. Published 2021.

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  8. Centers for Disease Control and Prevention. Pfizer-BioNTech COVID-19 Vaccine overview and safety. Updated May 27, 2021.