No, COVID-19 vaccines don’t impact fertility — here’s the science

Anti-vaccine activists and other conspiracy theorists have advanced several myths about COVID-19 vaccines. As a consequence, some people have chosen not to be vaccinated, putting themselves and those around them at unnecessary risk. One of the more prominent — and false — myths is that COVID-19 vaccines cause infertility. Where did this notion originate and how do we know it’s not true?

On Dec. 1, 2020, Drs. Wolfgang Wodarg and Michael Yeadon submitted a petition to the European Medicines Agency (EMA) requesting that emergency authorization for Pfizer’s mRNA vaccine be withheld because they believed it could cause infertility. Wodarg and Yeadon claimed that the SARS-CoV-2 spike protein, which is generated by COVID-19 vaccines, shares several short genetic sequences with a placental protein called syncytin-1 — a protein critical to the development of a healthy placenta. They argued that people immunized with mRNA vaccines would, therefore, develop antibodies that bound not only to SARS-CoV-2 virus but also to the placenta, leading to infertility or miscarriage.

Wodarg and Yeadon’s argument was flawed for several reasons.

First, the SARS-CoV-2 spike protein is immunologically distinct from syncytin-1. To say that these two proteins are disturbingly similar would the equivalent of saying that two people share the same social security number because both contain the number six.

Second, during the large, prospective, placebo-controlled studies of Pfizer’s and Moderna’s mRNA vaccines, 36 women became pregnant. If mRNA vaccines affected fertility, then most if not all of the pregnancies should have occurred in the placebo group, not the vaccine group. This wasn’t the case. The pregnancies were divided equally among vaccine and placebo recipients. In other words, mRNA vaccines neither enhanced nor disrupted fertility.

Third, if, as Wodarg and Yeadon argued, antibodies directed against SARS-CoV-2 spike protein could cause infertility, then antibodies against this protein following natural infection should do the same thing. At present, about 33 million Americans are reported to have been infected with SARS-CoV-2 virus. But those are just the people who have been tested and found to have been infected. Antibody surveillance studies have shown that the 33 million number is probably off by a factor of three. This means that about 100 million people have likely suffered COVID-19, virtually all of whom have made brisk antibody responses against the SARS-CoV-2 spike protein. So, what has happened to the birth rates in the United States? If Wodarg and Yeadon’s hypothesis was correct than the birth rate in the United States should have gone down dramatically. In fact, more than 3.5 million children were born in the U.S. in 2020, only a 4 percent decline from the previous year.

In short, all available evidence supports the notion that COVID-19 vaccines do not cause infertility. Unfortunately, while it is easy to scare people, it’s much harder to unscare them. It’s hard to unring the bell. Or, as noted by author Jonathan Swift, “falsehood flies, and truth comes limping after it, so that when men come to be undeceived, it is too late; the jest is over, and the tale hath had its effect.” For women of childbearing age who have chosen not to vaccinate because of this falsehood, the “tale that hath had its effect” could be not only possible unnecessary suffering — but even hospitalization and death from a preventable virus.

Paul A. Offit, MD, is the director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and a professor of Pediatrics at the Perelman School of Medicine at the University of Pennsylvania. He is also a voting member of the FDA’s Vaccine Advisory Committee. His upcoming book is “You Bet Your Life: From Blood Transfusions to Mass Vaccination, the Long and Risky History of Medical Innovation.”  Follow him on Twitter: @DrPaulOffit.