There is no evidence to show that Pfizer vaccine leads to infertility
List of claims
The vaccine has a spike protein, a slight part of which resembles Syncytin-1, a cell-cell fusion protein found in placenta. However, there is no scientific evidence to show that such a minute resemblance would not be enough for the immune system to attack the placenta and lead to infertility. Therefore, the claim in MISLEADING.
In a recent Facebook post, there are claims that the COVID-19 vaccine specifically the Pfizer vaccine will lead to infertility. At a time when there are nationwide vaccination drives that have begun across the globe, such claims are bound to heighten the hesitancy towards the vaccines. Let us fact-check the claim made in the post.
Source: Facebook post
The claim did a number of rounds on social media warning women to be wary of the vaccine if they wish to conceive. The basis of the claim stems from a protein known as a spike protein that is found on the surface of the SARS-COV-2 virus that causes the COVID-19. The Pfizer/BioNTech vaccines are mRNA vaccines, i.e., unlike the regular vaccines which confront the immune system with part of the weakened or deactivated virus, these mRNA vaccines give a ‘blueprint’ of a part of the virus (the spike protein) that the body can recognize and fight when confronted. This spike protein plays a vital role in the recognition of the virus and readies the immune system to attack the virus. These proteins are further made by building blocks of amino acids, and its combination/sequences of those that make up different proteins.
Therefore the Pfizer/BioNTech and Moderna COVID-19 vaccines, which are live vaccines provide instructions to the body to re-create this spike protein to generate an immune response system to attack the virus when affected. The present contention is that a small part of the spike protein resembles a part of another protein essential for the formation of the placenta, called syncytin-1. Syncytin-1 is vital for the placenta to remain attached to the uterus and act as the source of nutrition and blood supply of the fetus during pregnancy. However, the sequence of amino acids found in the spike protein and the syncytin-1 are not quite similar- in fact, the similarity is quite short- four shared amino acids do not form the same protein that gives rise to autoimmunity. The antibodies produced against COVID-19 spike protein will not block syncytin-1.
In a blog post authored by Edward Nirenberg, who is a graduate from Cornell with a degree in biological sciences and writes extensively on vaccines, the same has been explained that there are only two very small parts of the proteins which resemble each other. This in turn is not very significant enough to confuse the immune system to attack and stop the placenta formation.
Therefore, there is no suggestive evidence to suggest that the small resemblance in the amino acid sequence in the spike protein and syncytin-1 will lead to infertility in the short or long term in women. The same conclusion can be read here, here, here, and here.