Achieving herd immunity to Covid-19 has been made difficult by internet disinformation campaigns. One such speculative idea is that Covid-19 vaccines will cause infertility in both women and men. Recent studies have demonstrated that these fertility concerns over Covid-19 vaccines are unfounded and that Covid-19 itself is more likely to cause fertility issues in men.

The initial concern that Covid-19 vaccines could cause infertility in women stemmed from the observation that syncytin-1, a protein found in the placenta, has a small amount of homology to the SARS-CoV-2 spike protein. This idea was spread by a blog post made by a senior Pfizer employee, which suggested that Covid-19 antibodies from vaccines could attack the placenta. This disinformation led some young women to decline the vaccine over fertility concerns. The blog post has since been taken down and the homology between syncytin-1 and the SARS-CoV-2 spike protein is very low. There are only two 2-amino acid identities within 5-amino acid stretches for similarity search, which is incredibly unlikely to cause any cross-reactivity between the anti-SARS-CoV-2 antibodies and the human syncytin-1 protein.

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This lack of effect on fertility is further supported by the fact that there was no difference between the placebo and control groups for the number of female participants who became pregnant during the first Covid-19 vaccine trials. In addition, there was no difference between the rate of miscarriage of the control group and that of the vaccine group. The vaccines’ developmental and reproductive toxicity studies demonstrated no evidence of reducing rodent fertility. Covid-19 vaccination has not shown any observed effect on in vitro fertilisation via stimulated ovarian follicles, egg quality or implantation rates. Studies conducted on the Pfizer–BioNTech BNT162B2 Covid-19 vaccine have also shown that it does not elicit any cross-reacting antibodies to the human syncytin-1, despite its strong neutralising activity to the SARS-CoV-2 spike protein.

Evidence suggests that a Covid-19 infection is more likely to be dangerous to a pregnant woman’s health than the Covid-19 vaccine itself. The risk of contracting a Covid-19 infection during pregnancy could be more detrimental to a woman’s health and could be mitigated by receiving the Covid-19 vaccine. Pregnant women have a higher risk for intensive care unit admission due to Covid-19, and there is also the possibility of pre-term birth.

Recent studies on Moderna and Pfizer’s Covid-19 vaccines demonstrated a lack of effect on male fertility, with no evidence of an effect on any sperm parameters, including semen volume, sperm concentration, sperm motility and total motile sperm count. There is, however, evidence that Covid-19 infections can cause men to develop erectile dysfunction, possibly due to infection-induced damage to the blood supply to the penis, and some male Covid-19 patients report testicular or scrotal pain. In addition, SARS-CoV-2 has been found in male sperm months after the infection, and patients have been found to have reduced sperm count, possibly due to hormonal disruption.

The evidence indicates that Covid-19 infections pose a risk to male fertility, and people who are concerned about their fertility should get a Covid-19 vaccination to mitigate this risk, as there is no evidence of the vaccines affecting fertility in either men or women. Disinformation about the vaccines’ effects on fertility is hampering achieving herd immunity and endangering the lives and wellbeing of the people these campaigns purport to protect.