In the European Union, two vaccines have recently been approved against SARS-CoV-2 – bnt162b2 (from BioNTech/Pfizer) and mrna 1273 (from Moderna). The two rely on mRNA technology (mRNA vaccines), which is rather new and has not been widely used in humans beyond clinical trials. As these vaccines are to be used on a population scale, some concerns have been voiced. One of them is the question of whether a vaccination could have a negative impact on a child or mother during and after a pregnancy.

To start with, we need to make one point very clear: this article is not intended to give medical advice. We recommend that people consult qualified healthcare professionals in such matters; specifically, in case of the COVID-19 vaccine in a pregnancy context. The goal of this article is to summarise the available data on vaccinations during pregnancy and to discuss them in the context of the COVID-19 vaccine.

While the COVID-19 vaccine data on the subject is sparse it is important to mention some background information with regard to live vaccines (e.g. smallpox) and non-live vaccines (Tdap or COVID-19). It has been shown that vaccinating pregnant women with non-live vaccines (such as the flu vaccine and Tdap) is safe and effective [4, 5]. With the exception of smallpox and yellow fever vaccines, other ones can be safely administered to breastfeeding individuals. Both aforementioned vaccines contain live-attenuated viruses that are dangerous to a baby upon transmission [6]. It is also established that transplacental IgG antibodies are passed to an unborn during the last trimester and secretory IgA to a baby during breastfeeding. This gives the child temporary protection [11].

The only available studies directly investigating the impact of the COVID-19 vaccination on pregnancy or offspring come from animal research conducted by Moderna and BioNTech. Scientists did not observe any negative effects on rats’ fertility, pregnancy, or fetal/postnatal development. Antibodies against SARS-CoV-2 were detected in the foetuses and offspring. This does not necessarily translate to humans. No data is available on breastfeeding or the COVID-19 vaccine transfer to a foetus [2, 3]. 

Thus far, there is very little clinical data to back up any position on the subject. The important reason for this is that pregnancy is one of the important exclusion criteria in clinical trials unless it is a specifically targeted group. Pregnancy may happen during the course of a trial and volunteers are followed-up upon [1]. Notably, as of November 14 2020, 12 vaccinated BioNTech’s study volunteers (and 11 in the placebo group) reported a pregnancy. No unsolicited events, like spontaneous abortion were observed in the vaccinated group [2].

One concrete concern regarding the COVID-19 vaccine is that a part of the SAR-CoV-2 virus (Spike protein), which is produced by the mRNA vaccines, will cause issues with fertility or pregnancy due to the similarities with syncytins, which are proteins having a role in placental development in humans. Therefore, it is hypothesized that antibodies developed against Spike would attack syncytins, disrupting the placenta [7]. These concerns were not confirmed in the clinical studies nor via any protein similarity analysis to this date.

An individual’s decision about the procedure should be thoroughly discussed with their healthcare professionals. The benefits and risks will be weighed based on individual medical history and the state of the pregnancy. Potentially, a SARS-CoV-2 infection can carry a risk to a pregnant woman [8]. The WHO is reluctant to make such a recommendation [9] but national professional groups (such as the American College of Obstetricians and Gynecologist) stated that the choice should be made individually in each case [10]. The reason for such discrepancy is that a risk/benefit analysis based on such limited data is complex especially in the light of the pandemic. 

In summary, there is very limited data on the safety of mRNA-based vaccination against SARS-CoV-2 in pregnant or lactating women beyond pre-clinical studies. It is highly recommended to contact a trusted healthcare professional and get familiarized with the recommendations of the local authorities and expert groups on the matter before proceeding with any decision about vaccination.COVID-19