The issue of how COVID-19 vaccines may impact fertility and/or pregnancy continues to be live. Health Minister Robin Swann told the Stormont health committee on 14 January 2021, that an anti-vaccination group targeted young female healthcare staff outside vaccination centres, saying COVID-19 vaccination would affect their fertility. He added that this message was “quite negative, quite wrong, potentially quite damaging”. This was also reported in the local media.

These particular anti-vaccination campaigners are not alone in this view. Theories are being spread across social media, particularly about the Pfizer-BioNTech vaccine, about how a protein on the surface of the SARS-CoV-2 virus (the virus which causes COVID-19), called a “spike protein” works. 

This is where it gets a little complicated. 

The science bit — how an mRNA vaccine works

FactCheckNI has written before about how this vaccine works. The Pfizer-BioNTech COVID-19 vaccine is a messenger RNA (mRNA) vaccine. This type of vaccine does not put a weakened or inactivated germ into our bodies. Rather, an mRNA teaches our cells how to make a protein, or even just a piece of a protein, that triggers an immune response inside our bodies.The COVID-19 mRNA vaccines give instructions for our cells to make a harmless piece of what is called the “spike protein”, which is found on the surface of the virus that causes COVID-19. The immune system response to this vaccine — our body’s production of antibodies — is what protects us from getting the COVID-19 disease if the real virus enters our bodies.

How has this been linked to issues with fertility?

The misinformation and disinformation circulating about the impact of this mRNA vaccine on fertility often focus on a purported link between the spike protein formed by receiving the mRNA-based vaccines and blockage of a protein necessary for formation of and the  attachment of the human placenta to the uterus. The protein syncitin-1 is critical for the placenta to remain attached to the uterus and act as the source of nutrition and blood supply to the fetus during pregnancy. However, this is not the protein known as the COVID-19 “spike protein”. The antibodies produced against the COVID-19 spike protein will not block syncitin-1.

In short, an mRNA COVID-19 vaccine does not share an amino acid sequence with the spike protein of SARS-CoV-2 (which results in COVID-19) that will make the immune system attack both the spike protein of SARS-CoV-2 and a placental protein. Why? The COVID vaccine amino acid sequence is too short for the immune system for our bodies to confuse it with placental proteins. Hence, it has been stated that there is no reasonable basis to believe that vaccines against COVID-19/SARS-CoV-2 will affect fertility. The three most advanced vaccines (from Oxford/AstraZeneca, Pfizer/BioNTech and Moderna) all work by getting our own cells to make copies of the virus spike protein.
It’s also important to know that it has also been concluded that: 

  • the mRNA vaccines do not contain any virus particles;
  • within hours or days our bodies eliminate mRNA particles used in the vaccine, so these particles are unlikely to reach or cross the placenta; and
  • the immunity that a pregnant individual generates from vaccination can cross the placenta, and may help to keep the baby safe after birth.

The original clinical trials for the Pfizer-BioNTech vaccine did not include either people who were pregnant or lactating, and the company has said available data is so far “insufficient” to determine any risks to pregnancy posed by the vaccine. It is important to note that 23 people became pregnant after participating in Pfizer-BioNTech’s vaccine clinical trial, of which there are no known adverse effects of the vaccine. Pfizer reported one poor pregnancy outcome in someone in the control/placebo group – meaning they had not actually received the vaccine. 
Meanwhile, the Pfizer-BioNTech vaccine was tested on rats, prior to mating and during pregnancy. There were no vaccine-related effects recorded on fertility, pregnancy, or foetal or offspring development.

So why weren’t pregnant people included in the original vaccine trials

A Stanford researcher explains that women have traditionally been excluded from clinical trials, more generally. This is attributed to the fact that men were thought to be a more homogenous group, and one which did not have to to consider sex-based variables (such as hormone cycles) that might impact the medical conditions under consideration. Dr Heather Byers elaborates on this: 

In addition, pregnant women are still classified as a ‘vulnerable’ population for all research studies, so investigators must take additional steps to enroll them to ensure minimum risk. Also, the lack of data about what pregnant women can safely be exposed to leads to more uncertainty. So many investigators choose to exclude them, even if they might benefit from the study intervention.

The historical legacy of thalidomide (prescribed for morning sickness during the 1950s) and diethylstilbestrol (DES) (prescribed to prevent miscarriage from the 1940s to the 1970s) has continued to inform the view that pregnant people and their children are vulnerable and should be protected from clinical research trials. Therefore, pregnant people are still almost automatically excluded from clinical trials. 

In the context of the COVID-19 pandemic, some have questioned the rationale of this approach; the risks for pregnant people from COVID-19 are marked. Findings from Sweden indicate that pregnant people with COVID-19 were five-times more likely to be admitted to the intensive care unit and four-times more likely to receive mechanical ventilation compared with those who are not pregnant. 

What are the official recommendations for pregnant people regarding COVID-19 vaccines?





FactCheckNI have previously published a dedicated article about COVID-19 vaccines during pregnancy. 
Article originally was originally published on 20 January and updated on 5 August 2021.
