Do the COVID-19 mRNA vaccines cause infertility?

I previously discussed the safety of COVID-19 vaccination during pregnancy here. Since then, the Society of Obstetricians and Gynecologists  of Canada has updated their stance to more specifically endorse the approved COVID-19 mRNA vaccines during pregnancy and breastfeeding. The World Health Organization also endorses the use of the vaccines in pregnancy. It bears repeating: the COVID-19 vaccines (both Moderna and Pfizer/BioNTech) are safe and recommended during pregnancy.

 

However, a related concern has stirred a significant amount of controversy and is specifically relevant to our patient population trying to conceive: do the COVID-19 mRNA vaccines cause infertility?

 

Let’s unpack the origins of this rumor. It began when a German doctor and a former Pfizer employee wrote a letter to the European Medical Agency in December to delay the study and approval of the Pfizer/BioNTech vaccine. This went viral (no pun intended) through a blog with a funny name called “Health & Money News” since taken down but archived here. First of all, they state that the vaccine contains the syncitin-1 protein, which is clearly inaccurate. Both of the approved viruses are mRNA-based, thus do not contain any viral protein. Secondly, they argued that the target of the vaccines, the COVID-19 spike protein, was similar to syncytin-1, a human protein that is crucial to the connection between the placenta and the uterus. Therefore, they claimed, the antibodies produced against the COVID-19 would also attack syncitin-1 and could lead to “female sterilization”.

 

Fake news, or more specifically, fake science. While it turns out that the target of the vaccines, the COVID-19 spike protein, bears a passing resemblance to syncitin-1, there is no evidence that the antibodies elicited by the vaccine will even recognize the placental protein. An eloquent explanation by well-respected fertility experts illustrates that the amino-acid sequences of COVID-19 spike protein and syncitin-1 have very few similarities. The lack of homology between the COVID-19 spike protein and syncitin-1 is counterfactual to the baseless claim that the antibodies will cross-react and attack the developing placenta.

 

It is true that the vaccines were not tested on pregnant women or those trying to actively conceive, but there was some incidental evidence from the Pfizer/BioNTech trial: 23 women did get pregnant after the vaccine was administered, probably inadvertently. Twelve of these were in the vaccine group, and 11 in the placebo group. The only miscarriage occurred in the placebo group (see page 42 of the Pfizer/BioNTech FDA briefing), meaning this patient did not receive the actual vaccine.  Furthermore, according to this study even pregnant women actually infected with COVID-19 in the first trimester do not seem to be at higher risk for miscarriage, making the risk of miscarriage with the vaccine seem even less likely.

 

The bogus blog lacked evidence and distorted facts, but most importantly, has done a disservice to those who could be protected by the potentially life-saving vaccine. The risks of COVID-19 are real, and the benefits of the approved vaccines are proven. Trust science, not pseudoscience.