Can The COVID-19 mRNA Vaccines Cause Sterility In Females?

In an earlier blog post , we shared our thoughts on the life-saving mRNA vaccines and how they can impact your fertility.   We outlined the mRNA technology, the dangers of contracting COVID in pregnant women and cautioned on the myths circulating out in the social media world.

In this blog, we have some exciting news that we hope will further alleviate any hesitancy about getting vaccinated. 

A new study published by the American Society for Reproductive Medicine (ASRM) in their Fertility & Sterility Journal found that mRNA vaccines DO NOT cause sterility in females! This study conducted by Dr. Randy S. Morris further debunks the myths spread on social media and the digital ether that the vaccines would negatively affect reproductive-age women and their fertility.  

“Several reports claim that the purported similarity between syncytin-1 and the SARS-CoV-2 spike protein may induce immune cross-reactivity resulting in female sterility. We used frozen embryo transfer as a model for comparing the implantation rates between SARS-CoV-2 vaccine seropositive, infection seropositive, and seronegative women. No difference was found in serum hCG documented implantation rates or sustained implantation rates between the three groups. Reports claiming that COVID-19 vaccines or illness cause female sterility are unfounded.” 1

There’s a lot to unpack here, so let’s clarify what Dr. Morris’ groundbreaking study found in more layman terms. 

What Is Syncytin-1 And What Is Its Impact On Fertility?

Syncytin-1 is a cool little cell-fusion protein whose function is to aide the placenta. The placenta, in turn, helps the embryo to attach to your uterus and create a nutrient supply for your baby.  

The Baseless Claim

The claim made in December 2020 was that Syncytin-1 was similar in structure to the SARS-CoV-2 spike protein and since there were “similarities” between the two, that the mRNA vaccines could cause antibodies that damage not only the spike protein of COVID but also the Syncytin-1 protein.

First, the statements on the similarities being profound enough to cause sterility were baseless. The similarities between the two are not profound. Here comes the science: “Syncitin-1 is 538 amino acids long with a size of 73 kDa. The SARS-CoV-2 spike protein is 1,273 amino acids long with a size of 180–200 kDa. More importantly, the longest similar sequence of amino acids between the two proteins is four amino acids long.”2

This issue of “similarity” may best be succinctly put to bed by Dr. Paul Offit, Director of the Vaccine Education Center at the Children’s Hospital of Pennsylvania in an op-ed in the Washington Post: “To say that these two proteins are disturbingly similar would be the equivalent of saying that two people share the same social security number because both contain the number six”

On the claim that antibodies created by the disease or the vaccine caused sterility in females – researchers from Yale School of Medicine analyzed the reaction of 3000 proteins found in humans to the SARS Co-V2 antibodies including the syncytin protein. This award-winning research team evaluated the blood “…from  women with Covid-19 and did not detect any reaction between patients’ antibodies and the syncytin-1 protein”.  In a NY Times article, the Yale researchers also noted that “there is also no evidence or reports so far of infertility among women who have recovered from Covid-19, despite the millions who have been infected. To the contrary, women have conceived after coronavirus infection and vaccination.”

Human Clinical Data

If the laboratory analysis from Yale doesn’t sway you, Dr. Morris’ study should add more clarification and confirmation as it is the first to use human clinical data. The researchers performed 171 Frozen Embryo Transfers (FET) in the study period, of which 143 were used in the analysis.  

Frozen embryo transfer is one of the most revolutionary advances in Assisted Reproductive Medicine. The process basically flash freezes embryos, eggs & sperm, which are later, thawed and used in IVF transfers.  

In the published ASRM study, the team documented implantation rates in women who had the Moderna or Pfizer mRNA vaccines (SARS-CoV-2 vaccine seropositive), women that had contracted COVID and thus had antibodies (infection seropositive) and women that had not contracted the disease nor had been vaccinated (seronegative women). And guess what? They found no difference in the three groups.

As ASRM states: “This study documented, for the first time in women, that seropositivity to the SARS-CoV-2 spike protein – whether from vaccination or COVID infection – does not prevent embryo implantation or early pregnancy development. Physicians and other health professionals must counsel women of reproductive age that neither previous COVID-19 illness nor antibodies produced from vaccination to COVID-19 will cause sterility.”

This is all fabulous and reassuring news. We hope these more recent and highly respected studies help you start a dialogue with your medical team regarding the vaccines.  

Dr. Debbra A. Keegan, Dr. Jessica Salas Mann and Dr. Serena H. Chen receiving their COVID-19 Vaccines.

Our intention here at IRMS is to always protect our patients and we believe in the merits and science of the vaccines. The choice, however, is always yours. We are here to empower you with information without bias – as we stand by you in your fertility journey.  

For more information on COVID-19 and the various vaccines please feel free to contact us through our website, DM our social handles or by calling us at 973.548.9900


1 Randy S. Morris M.D. (2 June 2021). SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility. sciencedirect.com

2 Ibid. sciencedirect.com

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