In February, at the University of Illinois tweeted that she had got her period early and was bleeding heavily following her first dose of the Moderna coronavirus vaccine, and asked if others had experienced a similar thing. Such was the response online that just 21 minutes later, she had decided to set up a . Answers from that study will be forthcoming, but preliminary data from the UK shows that Clancy isn鈥檛 alone in noticing changes in menstruation patterns after a covid-19 vaccine.
What data do we have on covid-19 vaccines affecting menstruation?
Up to 17 May, nearly linked to covid-19 vaccination were made to the UK鈥檚 Medicines & Healthcare products Regulatory Agency (MHRA). People reported delayed or heavier periods and unexpected bleeding.
Which vaccines have been linked to period changes?
In total, 2734 reports mentioned the Oxford/AstraZeneca vaccine, 1158 were related to the Pfizer/BioNTech vaccine and 66 were linked to the Moderna vaccine, according to data seen by . However, the MHRA says the current evidence 鈥渄oes not suggest an increased risk of either menstrual disorders or unexpected vaginal bleeding following the vaccines鈥�.
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What could be causing heavier periods?
It could be part of the body鈥檚 normal immune response to vaccines. Obstetrician-gynaecologist Jen Gunter that immunisation could potentially lead to menstrual disturbance by causing inflammation of the endometrium 鈥� the uterine lining that is shed during a period. But she also suggests the link could be indirect or, perhaps, not exist.
Is it just a coincidence?
Given that these are new vaccines, we should be open-minded about potential side effects, says at the Royal College of Obstetricians and Gynaecologists in the UK. 鈥淗aving said that, many women at some point during their lives will go through a time where their periods become a bit unusual鈥� and of course, many, many women are having a vaccine. It could be just chance, or it could be cause and effect, but we just don鈥檛 know at the moment.鈥�
What else could explain this?
Stress, diet and exercise can all affect the menstrual cycle, so it isn鈥檛 unreasonable to think that the stressors of the pandemic could trigger changes in periods for some people. found that about half of 749 athletes reported changes to their menstrual cycles during lockdown. The authors say that stress was the main contributing factor 鈥� job security worries were associated with longer periods, for instance.
Do other vaccines affect periods?
There is a lack of scientific literature on the topic, though it has been seen in at least one instance. Menstruation changes after vaccination were noted more than 100 years ago. A recorded cases of menstrual disturbance in nurses following immunisation against typhoid, including periods that were early or late, more painful or missed altogether. 鈥淪imilar to today, the conclusions were, 鈥榳e鈥檙e not really sure if these are normal changes or if these are caused by the vaccine鈥�,鈥� says Leslie Farland at the University of Arizona.
How can we know for sure if covid-19 vaccines cause these changes?
We need to research it more. 鈥淭here鈥檚 a lot we don鈥檛 know,鈥� says Farland, who is undertaking a retrospective study to explore whether menstrual changes occur after covid-19 vaccination. She says the current situation is a sign we need to do 鈥渁 better job of systematically collecting information on menstrual health as well as reproductive health鈥� in clinical trials and public health surveillance.
Should vaccines be timed with the menstrual cycle to avoid any side effects?
The American College of Obstetricians and Gynecologists says that there is no reason for people to schedule vaccinations based on their menstrual cycle, and that you can receive vaccines while on your period. As ever, anyone experiencing unusual vaginal bleeding should seek medical advice, especially if they are post-menopausal.
Reference: medRxiv, DOI:
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