by Kristina Murkett
Tuesday, 20
July 2021

It’s time to talk about Covid vaccines and periods

Women have reported changes to their menstrual cycle after being jabbed
by Kristina Murkett

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 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.

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  • As a physician who works in a province of Canada with less than 1 million people, I personally know of or have looked after 3 myocarditis patients, 3 Guillain-Barre, 1 severe VITP, several cases of serious blood clots, as well as 3 cases of “COVID-arm” (a real thing, not a colloquial or hysterical description). It is nearly impossible to report a vaccine AE here, FB groups that tried to have people come together to share AE experience have been purged, and speaking at least for Canada, the message continues from “the authorities” that “vaccines are safe and everyone should get one”. Tell that to the 20-something healthy thin guy whose heart will never work the same, and whose risk for serious outcomes from COVID was essentially zero.
    I’m not an anti-vaxxer (I got mine), but I am pro-science.

  • Kristina Murkett is absolutely right in saying that breaking down trial data by sex is long overdue. She should be thanked for acknowledging that this is a problem that affects women and only women because of the very basic facts of female biology. Sex matters.
    The New York Times and The Guardian covered this story earlier in the spring. Both reports avoided using the word ‘woman’, e.g. “people who had menstrual cycles or a uterus reported menstrual irregularities after reporting exposure to tear gas”, “people who are pregnant”, “respondents who potentially menstruate.”

  • I read this twice, and excuse male ignorance, but I’m still not clear about what the purported ‘changes’ are. Delayed or missed periods? Heavier ones? More painful ones? I don’t doubt that there’s a problem here, but apart from registering the usual moan about the uncaring patriarchy (are there no women in medicine?), I’m none the wiser.

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