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New Study Seeks to Confirm That COVID-19 Vaccine Does Not Affect Male Fertility

Man and woman holding pregnancy test

Key Takeaways

  • The University of Miami is seeking male volunteers for a COVID-19 centric fertility study.
  • The study would track the motility and concentration of sperm to see how they are impacted by the mRNA vaccine.
  • Current research shows that the COVID-19 vaccine does not cause infertility, and researchers are hoping to confirm this.

Early into the pandemic, SARS‐CoV‐2 RNA was discovered in male semen. Many questions loomed, ranging from potential sexual transmission to effects on a fetus or fertility.

While these have all been debunked, there are now concerns looming around whether or not the COVID-19 vaccine could affect sperm quality. This is unlikely, but researchers are working fast to gather the empirical evidence necessary to eliminate any doubts regarding vaccine safety.

Goals of the Study

A study underway at the University of Miami is recruiting 60 male participants, ages 18-50. The study’s principal investigator, Ranjith Ramasamy, MD, associate professor and director of reproductive urology, tells us that, since vaccine production was rushed for “emergency use,” more research is needed. While Ramasamy hypothesizes that there will be no impact on male fertility, he is hoping for reassurance from the findings.

Ranjith Ramasamy, MD

“Based on the mechanism by which mRNA acts, we do not expect the COVID-19 vaccines will have an impact on male fertility. But obviously, we want data to confirm that hypothesis.

— Ranjith Ramasamy, MD

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 3-6 months thereafter.” 

“Based on the mechanism by which mRNA acts, we do not expect the COVID-19 vaccines will have an impact on male fertility. But obviously we want data to confirm that hypothesis."

How does the mRNA vaccine work?

Microbiologist and immunologist Andrea Love, PhD, has dedicated three podcasts to debunking vaccine myths, including one about infertility in women. 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.” The vaccine has yet to be tested on pregnant women, but pregnant women are not prohibited from receiving the vaccine. 

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. The hope is that, by the end of Ramasamy’s clinical trials, we will get confirmation of what scientists have presumed all along. 

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  1. Centers for Disease Control and Prevention. Information about the Pfizer-BioNTech COVID-19 Vaccine. Updated January 1, 2021.

  2. Centers for Disease Control and Prevention. Information about the Pfizer-BioNTech COVID-19 Vaccine. Updated January 1, 2021.