July 20, 2021 - 11:05am

Recently Pfizer and Moderna regulators announced that they would be adding heart inflammation as a potential side effect of their Covid vaccines. The European Medicines Agency found 145 cases of myocarditis and 138 cases of pericarditis out of 177m doses given of the Pfizer-BioNTech vaccine, and 19 cases of myocarditis and 19 cases of pericarditis out of 20 million doses given of the Moderna vaccine.

This is an important update, but it raises another question: why haven’t menstrual cycle changes been listed as a potential side effect too, given that over 13,000 women in the UK have reported this, and the true number is likely to be much higher?

Period changes may be a less dangerous side-effect, but it is nonetheless an important one. Firstly, misinformation about vaccines and fertility is rife (Google searches for infertility relating to Covid vaccines recently increased by 34,000% after anti-vaxxers spread false information from a petition by physicians questioning its safety), and not pre-warning women that they could experience menstrual changes only adds fuel to that fire.

Secondly, there has been a notable slow-down in the vaccine roll-out, especially amongst young people, and research shows that women are less likely to take up the vaccine than men. Thirdly, and most importantly, this is yet another example of society overlooking female health because we do not take into account the unique biological factors affecting women.

We know that Covid affects men and women differently, and yet neither the Pfizer or Moderna vaccine trials disaggregated data on adverse side effects by sex, and less than 0.2% of Covid clinical trials even mention sex as a recruitment criterion, according to the ClinicalTrials.gov database. Interestingly, a study back in March also reported that nearly all anaphylactic reactions to the Covid vaccines occurred in women, and almost all cases of blood clots caused by the Astra-Zeneca vaccine occurred in women under 55, and yet still the European Medicines Agency did not find any basis for reviewing sex as a specific risk factor.

We have known for years that women respond differently to vaccines than men; we tend to have stronger immune responses, both from antibodies and T-cells, and research on the flu vaccine suggests that women can produce the same immunological response to a half-dose vaccine as men do to a full dose. Surely this explains why women are so much more likely to experience adverse side effects (in Norway, 83% of reported side effects have come from women), and therefore makes this oversight even more bizarre.

The reasoning seems to be that taking into account women’s specific biological factors (for example, our fluctuating hormones) would complicate clinical trials, and therefore it is easier to see women as ‘little men’ rather than a discrete group with our own metabolic and hormonal differences. Yet the problem is that this leads to a kind of medical gaslighting; for example, telling women that changes to their period post-vaccine are ‘coincidental’ or purely ‘perceived’ not only invalidates their experiences but also dismisses the science. There are very plausible explanations for these changes — women’s uterus linings are linked to their immune system by chemical messengers called cytokines that regulate inflammation, and therefore may well be affected by vaccines.

If scientists really want to reassure women that these menstrual cycle changes are temporary, then they need data to back it up, and the problem is there simply isn’t any. This should not dissuade anyone from getting the vaccine — I had my second jab on Saturday — but it should be a wake-up call to organisations like The Wellcome Trust and The Medical Research Council that guidelines on breaking down trial data by sex is long overdue. Period.

Kristina Murkett is a freelance writer and English teacher.