Article by Olga Ocón Hernández, gynaecologist and Juan Rodés researcher from the Carlos III Health Institute at the San Cecilio de Granada University Clinical Hospital and the Biosanitary Research Institute of Granada (ibs.GRANADA).

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In early August, one of the periodic safety updates carried out by the European Medicines Agency (EMA) on Covid-19 vaccines reported menstrual disorders after vaccination and requested more information from the marketing agencies, pledging to review the available evidence and monitor this possible effect.

For its part, the Spanish Agency for Medicines and Health Products (AEMPS) also included this aspect in its seventh pharmacovigilance report on 20 July, stating that, so far, no causal relationship has been found between these alterations in menstrual periods and Covid-19 vaccines, although it does clarifies that this is still under study.

In this regard, a scientific study is being conducted at the University of Granada and the San Cecilio de Granada University Hospital, namely the EVA Project, led by Professor Laura Baena and aiming to assess whether vaccination is associated with this increasingly frequent consultation on menstrual disorders.

The study has three branches. The first is an online questionnaire that already has nearly 14,000 responses and is expected to be completed in September. Although the data are not definitive and have not yet been published, more than 70 % of the women involved reported changes in their periods after vaccination, including increased bleeding, more frequent bleeding, and delays inmenstruation, among other symptoms.

A second branch focuses on the one-year follow-up of slightly more than 100 women, starting before vaccination, and, if these disorders occur, on the possibility of characterising them. Of these women, at a time the study is not yet over, about 30 % report having some kind of alteration. In a third branch, blood tests are being carried out on a subgroup of these volunteers (before the first dose,between doses and after the last dose of vaccine) to try to study the biological mechanism that could be involved.

 Lack of understanding

The menstrual cycle and a self-perception of a normal menstrual pattern is one of the most important physiological processes for women's health, as its alteration is sometimes an early sign of other illnesses, although it can also be modified by external factors, such as lifestyle, psychological aspects, physical activity, and drug consumption, among other things. However, there is still a lack of understanding of menstrual physiology, as shown by in the lack of studies on this subject.

Covid-19 has affected more than 200 million people worldwide as of August. The disease is associated with severe effects, as shown by a high death rate and serious health sequelae. In addition, some studies have associated this viral infection with changes in sex hormone  levels among women and significant alterations in certain coagulation parameters.

However, research in this regard is still too scarce for one to infer a clear understanding of the mechanism and consequences of menstrual cycle disorders, especially given the lack of gender mainstreaming in scientific research, i.e. gender-differentiated research and subsequent gender analysis to understand the reasons for differences, if any. 

The first vaccines

One of themost important goals in the search for strategies to curb this pandemic has been the development of effective vaccines against the spread of the SARS-CoV-2 virus and a worldwide mass vaccination campaign.

The European Medicines Agency (EMA) has approved four vaccines based on randomised clinical trials: Pfizer/BioNTech,Moderna, AstraZeneca and Janssen. To date, 73.3 % of the population in Spain has received at least one dose of one of these vaccines. However, none of the leaflets of these vaccines contemplates the risk of menstrual alterations as a possible side effect of their administration. Scientific literature on the side effects of vaccination on women's reproductive health is extremely scarce.

Gender perspective

This may be due to the fact that possible alterations of this type are not usually included in studies on the adverse effects of vaccines. This brings us back to the lack of a scientific methodology with a gender perspective, particularly since 77 % of the side effects of the SARS-CoV-2 vaccines reported to the EMA have occurred in women.

We hope in the coming months to be able to provide more answers on the effect of these vaccines on menstrual health, so that it can be reported and included in the data sheet of the vaccines marketed along with the rest of known side effects, which could avoid unnecessary consultations and tests in women with these symptoms.

 It is also necessary to apply a gender perspective in health research, without simplifying the matter and attributing the health effects observed in women to stress or neuroticism, whether with Covid-19 or with other diseases or in clinical trials such as those carried out with vaccination against SARS-CoV-2. 

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This article is also available in Spanish.