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Home » COVID-19 mRNA vaccines do not cause infertility – another myth debunked

COVID-19 mRNA vaccines do not cause infertility – another myth debunked

Last updated on August 17th, 2021 at 10:32 am

Here we go again with another anti-vaccine myth about infertility and COVID-19 mRNA vaccines. The anti-vaccine zealots are so predictable. They grab onto a trope and hang on for dear life. They tried this nonsense with the HPV vaccine which was based on a retracted study, and they failed. They tried to claim that the tetanus vaccine caused “mass sterilization” in Africa, and they failed there too.

This time, it’s the COVID-19 mRNA vaccines from Pfizer and Moderna will cause infertility.  Anti-vaxxers are trying to use some seriously twisted “logic” to get from the facts about these vaccines to a major myth that somehow, in some magical way, these vaccines will cause infertility.

Let’s get right to the point – no, they don’t. But let me give you the science.

How did this myth start?

This strange myth about COVID-19 mRNA vaccines and infertility seems to have originated with Dr. Michael Yeadon, who claims to be the former head of respiratory research at Pfizer, and Dr. Wolfgang Wodarg.

In early December 2020, numerous memes and scary social media posts stated the “head of Pfizer research” had warned that Pfizer’s new COVID-19 mRNA vaccine would cause sterilization in women. We discussed this previously in detail, but this deserves its own little section.

Yeadon, a former employee of Pfizer, and NOT its head of research sent a letter to the European Medicines Agency (EMA), which is the FDA for the European Union. His title at Pfizer was vice president and chief scientist for allergy and respiratory.

This does not mean he knows anything about vaccines, about mRNA vaccines specifically, or about Pfizer’s vaccine development process. We’ve seen this before with anti-vaxxers – they make false authorities out of people who really have no actual knowledge of vaccines beyond spelling the word.

According to Snopes,

Yeadon and German physician Wolfgang Wodarg sent a letter to the European Medicines Agency, calling on EMA to halt clinical trials of Pfizer’s COVID-19 vaccine in the European Union. In the letter, Wodarg and Yeadon stated that the Pfizer vaccine blocks a protein that is key in the formation of the placenta in mammals, and they claimed that it’s possible women who receive the vaccine could become infertile. However, they did not state as fact that the vaccine causes sterility, as the Health and Money News headline suggests.

David Gorski, in a post on Science-Based Medicine, ripped this letter into tiny little shreds like a CIA-quality shredder. He also stated that “Yeadon is a COVID-19 denialist and conspiracy theorist.” Yeadon supported the Great Barring Declaration, which just wanted people to die to get herd immunity to COVID-19.

Yeadon may have been a good scientist at Pfizer, though it’s hard to tell. Who knows why he’s no longer there. But he’s gone off the deep-end of anti-vax disinformation, COVID-19 denialism, and full-on conspiracy theories. He lacks credibility in vaccines, and he’s pushing a completely debunked false narrative about fertility and the mRNA vaccines.

Yeadon is a crank that should be ignored. Period.

Do the COVID-19 mRNA vaccines cause infertility?

Basically, the myth is based upon a protein subunit on the S-protein that is “homologous” to the syncytin-1 protein that facilitates the development of the placenta. Hypothetically, if the syncytin-1 and SARS-CoV-2 spike proteins were similar or exactly alike, there could be some cross-reactivity of antibodies between the S-protein and the syncytin-1 protein.

This is one of those types of myths that has a tiny bit of biological plausibility, but in reality, there is no scientific evidence that it is true.

Syncytin-1 is an endogenous retroviral element that is the remnant of a 25 million year ago retroviral infection integrated into the old-world primates, which would eventually include humans. In other words, it was incorporated into our genome as a result of retrovirus infection. As I wrote above, retroviruses can change our DNA.

In case you don’t know, the evolution of all organisms includes the incorporation of viral DNA into our genome. Occasionally, these viral genes confer some increased fitness, as in the case of syncytin-1 it becomes a part of placental development. About 8% of the human DNA comes from viruses during our long evolutionary past.

This is where it gets somewhat complicated. Even though coronaviruses are not retroviruses, viruses frequently share similar peptides (which are much smaller than proteins, only containing between 2 and 50 amino acids). There is one small peptide within the syncytin-1 protein that is homologous to one small peptide in the S-protein.

This peptide is called “CP-1”, and it contains about 3 amino acids. Syncytin-1 has 538 amino acids. The S-protein contains 510 amino acids. In other words, the CP-1 peptide is a tiny part of the structure of each of those proteins.

The immune system generally doesn’t recognize small peptides as antigens, because they are so small and because they are so similar to other peptides. An example of this is insulin – it is a small peptide that is found in almost all animals from crabs to humans. Before we made human insulin, we treated type 1 diabetes with porcine and bovine insulin, and the immune system just thought it was human insulin, despite the differences in the peptides.

But there are three critical points that should be emphasized:

  1. There is simply no published evidence (as far as I could find) that there is some immune cross-reactivity between the S-protein and syncytin-1. Not only is there no evidence, but it’s also not plausible that one small 3-peptide part of those two proteins would induce some sort of cross-reactivity.
  2. Women have contracted COVID-19, and there aren’t any reports of sudden infertility risks. Remember, the S-protein that is being produced by the mRNA vaccines is the same S-protein in the SARS-CoV-2 virus. If this hypothesis being pushed by anti-vaxxers were true, then it would also be true with “natural” infection.
  3. If I’m totally wrong, and there is some weird cross-reactivity between 3 amino acid peptides, then there’s more reason to get the vaccine to prevent an infection.

My friend Edward Nirenberg, who makes my scientific geekiness seem lame, also busted this ridiculous myth with some intense science. So between Dr. Nirenberg and I, can we take this particular myth and throw it into the wastebin of anti-vax tropes?

Dr. Nirenberg wrote:

Someone has claimed that the COVID-19 vaccines are going to cause infertility because of a shared amino acid sequence in the spike protein of SARS-CoV-2 and a placental protein, which will make the immune system attack both as it can’t tell the difference.

The truth? This sequence is too short for the immune system to meaningfully confuse it with placental proteins. It’s sort of like saying that you are going to be confused with a criminal because you wear a commonly sold red bracelet that was also found on the criminal. It’s not realistic. If this were true, we would also expect COVID-19 to cause early pregnancy loss a significant amount of the time. The evidence available to us does not support that this is the case.

There is no reasonable basis to believe that vaccines against COVID-19/SARS-CoV-2 will affect fertility.

But there’s more. If you just look at any random protein and compare it to the S-protein, guess what you’re going to find? Yes, out of hundreds of amino acids in any protein sequence, there is usually a sequence of maybe 3-4 amino acids that will match.

Orac wrote his article about this topic to remind all of us that “fertility” is a go-to strategy for every vaccine that has been launched over the past few years. The upcoming (I hope) Lyme disease vaccine will be the next target – you read it here first.

COVID-19 mrna vaccines infertility


The facts are that there is no evidence that the COVID-19 mRNA vaccines will have any effect on infertility. This is just another myth pushed by the anti-vaccine mob to cause fear, uncertainty, and doubt about these vaccines.

Let’s stick with scientific facts.


Amusingly, I was intending to post this article a few weeks ago, but I completely forgot. I used bits and pieces of it in other articles, but I wanted to make sure this whole story was in one place, and here it is.


Michael Simpson
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