After her first Pfizer vaccine five months ago, Dahye Yim, 30, noticed something different with her menstrual cycle.
Unusually heavier and with more physical symptoms such as a migraine, she went online to see if other women had experienced post-vaccine cyclical changes.
She uncovered similar stories but failed to find scientifically-backed information on possible short-term vaccine side effects.
The South Korean national, a PhD student based between London and Berlin, told Al Jazeera: “After I received my second dose in September, I noticed a lump under my armpit and I was able to find out very easily that this was a side effect that was nothing to worry about. This helped me calm down.
“It would have been helpful if this had been the case when I looked up information about menstrual cycle irregularities too. There’s a lot of money out there for COVID research and I know there are priorities, but I do think women’s health is a big priority.”
‘Lack of knowledge and attention’
Thousands of other women have reported temporary changes to their regular menstrual patterns, including delays, heavier vaginal bleeding or more physical pain.
Irregularities have been reported with all vaccines and in various countries.
Initially, medical professionals played down the claims, stating that the number of reported cases was too low, or that the changes could be down to other factors such as pandemic-related stress.
Analysts say such a position deterred some women from getting the vaccine.
It also added to the echo chamber of misinformation and conspiracy theories surrounding the shots, including the most prominent falsehood – that a jab would lead to infertility.
Yet following a chorus of calls, efforts are now under way to investigate potential links.
Those reviewing the issue include the UK’s Medicines and Healthcare products Regulatory Agency (MHRA), after it received reports by more than 30,000 women and two US-based medical researchers who have collected more than 140,000 reports so far.
The National Institutes Health (NIH), the US government’s primary public health research agency, last month gave grants totalling $1.67m to five national institutions to look into the matter.
According to UNICEF, approximately 26 percent of the global population is of menstruating age.
Meanwhile, as the pandemic pushes periods into the spotlight, questions are now being asked about why there is so little knowledge about how vaccines can affect a woman’s menstrual cycle.
And more widely, how far these latest developments could serve as a turning point around how menstrual cycles and women’s sexual and reproductive health will factor into medical research going forward.
Maya Dusenbery, an American journalist and the author of Doing Harm: The Truth About How Bad Medicine and Lazy Science Leave Women Dismissed, Misdiagnosed, and Sick, based in Oregon, told Al Jazeera: “The issue really raises some of the broader problems when it comes to women’s medical care. Within the COVID-19 vaccine trials, there just isn’t that sort of awareness that half of the population menstruates, and that it’s a normal part of their regular health experience. This lack of knowledge and attention adds to the broader culture of misinformation about the vaccines which could have been avoided easily from the get-go.”
During COVID-19 clinical trials, women participants say they were not asked about their periods.
“It is understandable that they didn’t ask this question because they tried to bring the vaccine as quickly and safely as they could. There was an expedited approval process to get it out and get it to us, which is scientifically sound,” said Dr Mostafa Borahay, the director of general gynaecology and obstetrics at Johns Hopkins Bayview Medical Center, in Maryland, US, and one of the NIH grant recipients.
In the past, menstrual cycles irregularities have been recorded as post-vaccine symptoms in other studies, including in human papillomavirus or HPV vaccine trials conducted in Japan in 2010 and 2013 that noted an “abnormal amount of menstrual bleeding” in some participants, and in US-based influenza vaccination trials that ran between 2013 and 2017.
Yet beyond a few records, there is very little data or scientifically backed knowledge on how vaccines might impact a woman’s menstrual cycle.
“There has been a historical squeamishness around periods, and we absorb that from our environment,” Dr Victoria Male, a lecturer in reproductive immunology at London’s Imperial College, told Al Jazeera.
“There are many people who don’t call it period and use terms like flow or time of the month. All of that feeds into a situation where we don’t really feel comfortable talking about menstruation.”
She said that in future, trial participants should be asked about their periods “as a standard question”.
‘Spotlight on pre-existing problems’
Structural gender imbalances around funding and the underrepresentation of women, as researchers and participants, also play a role, say analysts.
It is only recently that female participants have been examined in clinical trials – the NIH, the recent grant giver, only required women to be included as recently as 1993, previously excluding women because the gender group was considered too complex to study because of their hormone changes.
In the UK in recent years, less than 2.5 percent of publicly funded research has gone to projects around reproductive health. Yet figures show that one in three women will suffer from a reproductive or gynaecological health problem in their lifetime.
For women of colour, the issue is life-threatening.
Black women are four times more likely – and women from Asian ethnic backgrounds are twice as likely – to die in childbirth compared with their white counterparts.
“Even today, women are still underrepresented as researchers in the medical field and generally, those who don’t personally experience something are less likely to think, study or ask about it,” said Dusenbery. “As a result, women’s sexual and reproductive health conditions, and more generally, health issues that disproportionately affect women, tend to be under-researched, and when that happens we don’t get a full picture of what is happening. It then creates downstream effects, like with the COVID vaccines, that could have been avoided.”
Analysts say that the silver lining is that more focus is now being given to women’s sexual and reproductive health in medical research.
Dr Borahay said that in one of his studies, he will be working with a period-tracking app that will provide data on thousands of women, with preliminary findings due out later this year.
Dusenbery, the author, said: “This pandemic has offered a lot of opportunities to put a spotlight on a lot of pre-existing problems within the medical system.
“Women and men, on average, tend to experience differences when it comes to the same disease and the same treatment, and we need to be designing our research to figure out those differences and when they might matter.”