Why Is My Period Late After Getting The Covid-19 Vaccine?

By now, we’ve all seen plenty of memes about “hot vaxx summer” — that is, the period of relative freedom supposedly coming our way, made possible by access to Covid-19 vaccines. After almost 1.5 years of living under pandemic restrictions that have governed nearly every area of our lives, and all the while having experienced a scale of loss previously unimaginable for most of us, the vaccine looks a lot like hope. A lot like freedom. 

For those of us lucky enough to live in countries where vaccine supply has been adequate to inoculate most — if not all — of the adult population, the promise of an end to restrictions and the return to a world in which we don’t need to worry so much about friends and family who are more vulnerable comes as both a welcome relief and a powerful motivator to get jabbed. And so we did. In the UK alone, 79.5m doses of Covid-19 vaccines have been given, and 34m are fully vaccinated.

As with all medicines, some people have noted experiencing a variety of different side effects after receiving their jabs — although, it’s important to note, these are not serious in the majority of cases and often last only a day or two. Typically, these can include having a sore arm around the vaccination site, flu-like symptoms, muscle aches or fatigue. Lesser discussed though, is that among the population of women and people who menstruate, some have noticed changes in period length, heaviness or frequency — and shared their experiences online.

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“I was meant to get my period a few days after my second jab but on the day nothing happened,” says 29-year-old Marie Le Conte. “There was nothing the day after that, or the day after that; I ended up starting to panic after day 5 of nothing, then on day 6 my period finally started. My cycle is usually like clockwork so I have to assume the vaccine had something to do with it.” Lisa Valentine, 38, experienced something similar. A few days after her second dose, Lisa “started having cramps and bleeding heavily.” Twenty-four-year-old Sophie Thompson also found her periods were disrupted. “Before my vaccination, I had been coming on within a 1-2 day window every month for around 6 months,” she says. “This changed the day I had my first dose of the vaccine, as I started bleeding 6 days earlier than my period was due, quite literally within a few hours of having the jab.” 

So what is going on? Why might our periods be going a bit haywire because of the vaccine? And should we be concerned about it?

No, is the simple answer, according to Dr Sue Ward, vice president at the Royal College of Obstetricians and Gynaecologists. “We’re aware some women have been reporting a change to their period cycle or symptoms during the pandemic,” Dr Ward says. “The degree to which changing hormone levels will affect someone is often informed by [their] psychological wellbeing at that time. We know that life events can make PMS symptoms feel worse and something as all-consuming and life-changing as a global pandemic could result in women experiencing their periods differently.”

Dr Belinda Coker, a physician specialising in women’s health, agrees. “An occasional change in a woman's menstrual cycle, such as skipping a period, or having a very light or very heavy period, can occur at any point in life,” she says. “Sometimes it's related to stress, acute illness, an immune reaction affecting hormone levels or lack of ovulation during that month. If it's an isolated event and periods return back to normal, there is no need for investigation nor any concern related to your reproductive systems and your future fertility.”

Dr Coker says that a number of people have reported menstrual changes after receiving the Covid-19 vaccine, such as a period that is heavier than normal or a period that is slightly later than usual. “The reason is not entirely clear, as menstrual cycle data was not collected during the trials and has not been formally recorded since the rollout of the vaccine,” says Dr Coker. It’s hard, therefore, to understand why some women might experience changes to their periods, she says, but she believes it “may be due to the immune response that is occurring to produce the protective antibodies against Covid-19.” She continues: “In some women, the immune response may temporarily affect hormone levels.” Given that our hormones affect our menstruation, this may explain the issue.

Dr Ward’s colleague, Dr Pat O’Brien, adds more reassurance, and emphasises that this does not mean that the vaccines (as many anti-vaxxers would have you believe) will affect your fertility. “We also want to stress that these perceived changes in menstrual cycle after having the Covid-19 vaccine should not be confused with an impact on fertility and the ability to have children. There is no evidence to suggest that Covid-19 vaccines will affect fertility.” Dr Coker is in agreement. “The evidence published from trials and since vaccines have been rolled out to the public supports that women do become pregnant after having the full course of the vaccine.” 

All experts agree that none of this should put you off having the vaccine. "It’s important to remember these side effects are mild and should not deter women from having the vaccine when they are called,” says Dr O’Brien. “Many women will experience a temporary change in their periods from time to time during their lives. And right now, many women in their 30s [and 20s] are having the Covid vaccine. So it seems inevitable that in some women these two events will coincide by chance.” Nonetheless, Dr Ward advises that if the changes persist or you have any new vaginal bleeding after the menopause, you should see your doctor.

Lisa doesn’t regret having her vaccine. “As inconvenient as this is, I have no worries about the vaccine,” she says, before explaining that at the time she “looked online to find explanations.” Sophie did the same thing. “Having read a few bits online on the BBC and in Vogue about women experiencing irregular bleeding post-vaccine, I wasn't too panicked by this, but I was disappointed that I hadn't been told about any potential side effects of this kind and, indeed, that none were noted on the post-vaccine info leaflets,” she says. “I was glad that I'd taken the time to look into what other women had been saying before getting my jab, otherwise I would have been quite concerned.” Though both Sophie and Lisa experienced heavier bleeds, Marie’s next period was different. “It ended up being lighter than usual, which was a nice silver lining,” she explains.

What is clear is that a lack of data is impeding women’s access to information about the vaccine’s potential side effects regarding menstruation (to help to reverse this, you can contribute to Dr Kate Clancy’s research here). In the meantime, remember that you are absolutely entitled to ask questions about the vaccine either to your doctor or the person giving you the vaccine, and, if it helps, to read about the subject — but remember to stick to trustworthy sources of information (like the BBC).

And don’t panic! Everybody — and every single body — is different, and after the most anxiety-inducing year of our lives, remember that any changes to cycle length or appearance aren’t necessarily an indication that something is wrong. Seek medical care if you need it, and go out there and get vaccinated!

Update Jan 24, 2022:

A recent study published in the journal Obstetrics & Gynecology confirms there is a correlation between the COVID-19 vaccine and fluctuations in the menstrual cycle. The study analyzed data provided by Natural Cycles- a menstrual cycle tracking app. Researchers looked at records from nearly 4,000 people - around 2,400 of those users were vaccinated against COVID-19; 1,550 were not.

What the researchers found is that vaccination was associated with, on average, less than one day’s change in cycle length. Worth mentioning is that a number of people who received both doses of the vaccines experienced a change of at least two days. Almost 10% of these people noticed a more significant change and recorded their cycles were eight days longer than expected, too. The unvaccinated group did not experience any difference.