In December 2020, a blog post appeared online claiming, falsely,
that a senior employee at Pfizer was concerned that antibodies elicited by COVID-19 vaccines
could attack the placenta. The post was quickly removed
but the rumours that it started continue to spread and
a survey carried out by ‘Find Out Now’ found that
more than a quarter of young women in the United
Kingdom would decline the vaccine, citing concerns
about its effect on fertility. This is not the first time that
unfounded rumours about vaccines causing infertility
have circulated. In 2003, such concerns resulted in a
boycott of polio vaccination in northern Nigeria; more
recently, they have contributed to hesitance in accepting
the human papillomavirus vaccine. It is understandable
that people are apprehensive, especially about a new vaccine:
the vast majority of adverse events can be ruled out
in clinical trials, but the short time frame during which
these take place, especially for COVID-19, means that
events that could potentially occur decades into the
future are harder to discount. Indeed, many people are
hesitant specifically about receiving an mRNA vaccine,
as this is a relatively new platform. With respect to these
concerns, it is worth noting that the first human trials
of mRNA vaccines began in 2006, so there have been
15 years during which any long-term problems arising
from the platform itself could have come to light1
.
Although many of the rumours that COVID-19 vaccines
might damage fertility centre specifically on the
mRNA platform, probably because they first emerged in
the context of the Pfizer/BioNTech vaccine, the specific
claim is that antibodies recognizing the SARS-CoV-2
spike protein can cross-react with the human placental
protein syncytin 1 and thereby damage the placenta. If
such cross-reactivity did occur, vaccines on all platforms,
as well as natural infections, would be expected to be
associated with placental pathology. A natural experiment
assures us that this is unlikely to be the case as
people who are infected with SARS-CoV-2 shortly before
conceiving or early in pregnancy are no more likely to
miscarry than their uninfected peers. Nonetheless,
immunologists have also taken formal approaches to
address the claim that antibodies to spike protein could
cross-react with syncytin 1: there is no significant similarity
between the amino acid sequences of SARS-CoV-2
spike protein and syncytin 1 and convalescent serum
from patients with COVID-19 does not react with syncytin 1 (ref.3).
But the data that speak most clearly to the question
of whether the COVID-19 vaccines harm fertility come
from the clinical trials themselves. Developmental and
reproductive toxicity studies show that the vaccines do
not prevent female rodents becoming pregnant or harm
the pups if given during pregnancy. We also have an idea
of how the vaccines affect pregnancy in humans from
the volunteers who became pregnant during the clinical trials.
Pregnant people were excluded from the trials
and participants were asked to avoid becoming pregnant,
but, nonetheless, 57 pregnancies occurred across the trials
of the three vaccines that have so far been approved
in the UK. The outcomes of these pregnancies, so far as
they have progressed, are summarized in Table 1. There
was no significant difference in the rate of accidental
pregnancies in the vaccinated groups compared with the
control groups, which indicates that the vaccines do not
prevent pregnancy in humans. Similarly, the miscarriage
rates are comparable between the groups, indicating no
detrimental effect of vaccination on early pregnancy.
https://www.nature.com/articles/s41577-021-00525-y.pdf
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