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Does the Covid Vaccine Make Periods Irregular?

covid vaccine and irregular period
The truth behind the rumour  


Does the Covid vaccine make periods irregular? The truth behind the rumour

Headaches, tiredness, and a sore arm – these are some of the common, short-term side-effects of the COVID-19 vaccine that the public know.

And frankly, even the more miserable fallout – fever, nausea, headaches, and muscle pain – was well worth it in the end.

However, it seems that temporary changes to the menstrual cycle might be another side-effect – as reported by many women.

Dr Kate Clancy of the University of Illinois shared on Twitter that after receiving her first dose of Moderna, she was ‘gushing’ like she was in her 20s again.

Plenty of others have been sharing similar experiences on social media too.

We’re likely still some time away from knowing the scientific research and facts behind changes to menstrual cycles. In the UK, for example, tens of thousands of women have reported menstrual changes after getting the AstraZeneca vaccine. A smaller number citing differences after the Pfizer vaccine and Moderna jab.

Some women say they have had heavier bleeding than usual, with some saying their period arrived later/earlier than expected. It is important to note, however, that the changes seem temporary, with most saying their periods returned to regular schedules quickly.

But why is it happening at all?

Immunologist Dr Viki Male confirmed to the BBC that women report having a ‘heavier period than usual or a slightly delayed period’.

Dr Male said that where changes occur, they only last for “one or two cycles” and are likely caused due to hormones in our bodies being affected by our immune system and vice versa.

“Of course, it’s your sex hormones that are running your periods,” she explained. “If we give your immune system a big shock, whether we’re giving it to you via a vaccine or because you’ve got infected, you might see changes in those hormones.”

Does the covid vaccine make your periods irregular though?

Does the Covid Vaccine make periods irregular? 

Other experts reckon the link is purely coincidental. After all, most women experience changes in bleeding at some point. So it makes sense that these changes could occur after a COVID-19 jab.

Dr Pat O’Brien of the Royal College of Obstetricians and Gynaecologists highlighted: 

“Many women will experience a temporary change in their periods from time to time during their lives.

and right now, many women in their 20s and 30s have the Covid vaccine. So it seems inevitable that in some women, these two events will coincide by chance.”

Dr O’Brien added that the side effects “[…]are mild and should not deter women from having the vaccine”.

There is also no evidence to suggest that any of the COVID vaccines affect fertility. However, we know that this strain of coronavirus can be dangerous for pregnant mothers and unborn children. Sadly a small number of stillbirths in Ireland have been linked to a condition called Covid placentitis.

Let’s also consider the other factors that can impact our menstrual cycle – stress, anxiety, dietary changes, weight gain/loss, depression, environmental changes. These are all factors that have been more apparent for women during the lockdown and the pandemic in general.

Our recommendation 

As always, KeyForHer recommends that you see your GP if you have any pressing concerns about your menstrual health or cycle.

“Imagine if you didn’t know that fever could be a vaccine side effect?” gynaecologist Dr Jen Gunter explained. “You might be concerned that something untoward was happening to your body when all you were experiencing was a typical post-vaccine fever. That is exactly the same with menstrual irregularities.”


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