Why The Covid Vaccine Might Impact Your Periods

The changes are likely to be small and short-lived, so don't panic.
Anna Blazhuk via Getty Images

Noticed changes to your period after the Covid vaccine? Don’t panic.

“Changes to the menstrual cycle do occur following vaccination,” a leading menstruation expert has said. “But they are small compared with natural variation and quickly reverse.”

Dr Victoria Male, from Imperial College London, spoke about the concerns some women have had around the vaccine, periods and fertility in a British Medical Journal editorial.

She said “misinformation” was to blame for causing women unnecessary worry and that there is no evidence the vaccines impact fertility. The changes to periods are also very small and short-lived.

Dr Male pointed to two large studies on the subject – one from the US and one form Norway – and called the results “reassuring”.

A first study from the period tracking app Natural Cycles analysed the menstrual cycles of nearly 4,000 US women to see if vaccinations had an impact on their periods.

The study, published in the journal Obstetrics & Gynaecology, concluded that women who had the vaccine appeared to have a small change in cycle length after the jab. Menstrual cycles were on average one day longer for vaccinated women when compared with their three pre-vaccination cycles. No change was noted among unvaccinated women.

The second study of more than 5,600 people in Norway highlighted how periods change naturally, anyway. Nearly 40% of respondents reported changes to their periods prior to vaccination – and we know that stress can cause delays or changes to periods. Who hasn’t been stressed in the pandemic?

It’s reassuring to know that any changes that do happen t periods are short-lived after the vaccine, but why might they occur in the first place?

Dr Nighat Arif, a GP specialising in women’s health and family planning, tells HuffPost UK these changes are temporary and shouldn’t deter women from having the vaccine.

“After millions of doses of the vaccine being given across the globe, there’s no evidence the Covid-19 vaccine causes long-term problems with your periods and it does not affect your fertility,” she says.

“It’s important to understand that the lining of the womb is where the immune system sits. So, just like having a temperature, a headache, aches and pains is a side effect of any vaccine because it triggers the immune system – the same immune response happens in the womb lining.”

You might experience an irregular period, a heavy period or a missed period after the vaccine due to the immune response, but this is temporary, she adds.

“Our cycles vary due to so many factors such as stress, diet, weight changes but actually, catching Covid-19 has a very good chance of messing with your menstrual cycle, so the best way to protect your overall health and your cycles is to get vaccinated,” she says.

Yes- I have done a TikTok answering the query around vaccines affecting periods. pic.twitter.com/HMZ5zlg97l

— 𝑫𝒓 𝑵𝒊𝒈𝒉𝒂𝒕 𝑨𝒓𝒊𝒇 (@DrNighatArif) June 2, 2021

Other leading doctors have urged women not to panic at reports of altered periods. “It’s important to remember these side effects are mild and shouldn’t deter women from having the vaccine,” said Dr Pat O’Brien, vice president at the Royal College of Obstetricians and Gynaecologists (RCOG).

“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 are having the Covid vaccine. So it seems inevitable that in some women, these two events will coincide by chance.

“If, however, these changes persist, or you have any new vaginal bleeding after the menopause, you should see your doctor.”

Dr O’Brien reiterated there is no evidence to suggest Covid-19 vaccines will affect fertility.

More than 36 000 reports of menstrual changes or unexpected vaginal bleeding following covid-19 vaccination have so far been made to the yellow card surveillance scheme run by the UK Medicine and Healthcare Products Regulatory Agency (MHRA).

But as cycles vary naturally and the MHRA does not collect comparison data from unvaccinated people, this cannot be used to establish whether menstrual changes increase after vaccination.

You can report any suspected side effects of the vaccines, as well as any medicines, via the ‘yellow card’ system, here.