TORONTO -- People have taken to social media to report menstrual changes after getting the COVID-19 vaccine, and while the jury is still out on if it’s directly related to the vaccine, experts say it is because women have more robust immune responses to vaccinations.

Women’s health and immunology experts are hesitant to say if menstrual changes are a result of the COVID-19 vaccine until further research is conducted, but noted that the added stress of the pandemic may contribute to shifts in one’s menstrual cycle.

“I think it's likely attribution. In other words, when two things happen, we tend to think they're related, and they may not be,” Dr. Jerilynn Prior, professor of endocrinology at the University of British Columbia and Scientific Director of the Center for Menstrual Cycle and Ovulation Research, told in a Zoom interview.

Some of the reports she’s seeing from people on social media are happening too quickly to be linked she added.

“The interactions of the immune system and the menstrual cycle don't happen overnight,” she said. “They are longer term things.”

It doesn’t seem likely to Prior that the vaccine would set off menstrual changes, but she said that does not mean the reports should be ignored.

“I think it highly unlikely. That doesn't mean it doesn't need studying, but I don't understand a physiology that would explain it,” Prior said.

Menstrual changes can happen for a number of reasons, one of which is stress, which many people have been under since the coronavirus pandemic started.

“There are lots and lots of reasons other than adverse effects of the vaccine that might alter menstrual cycle[s],” she said. “The main thing that alters menstrual cycles is the stress of living in a pandemic, of being isolated, of not having the hugs that you’re used to.”

The sheer relief of being able to get vaccinated could also lead to adjustment’s in one’s cycle.

“I think it's reasonably likely that the stress of the time and then the… anxieties around getting the vaccine for some people may be associated with this,” University of Toronto professor Jayne Danska told in a telephone interview on Friday.

Of the data collected on menstrual cycles during the pandemic, experts say it reflects more disruptions than usual.

“The pandemic, not surprisingly, has disrupted menstrual cycles at twice the ‘normal’ rate – not surprising given that it has been a stressful year and stress impacts menstrual cycles,” Liisa Galea, professor of psychology at the University of British Columbia, told in an email on Thursday.

Galea said it has been difficult to find information that’s been more than anecdotal, but she isn’t surprised by that.

“Female ‘only’ studies are at around 6 per cent, while male ‘only’ are around 40 per cent depending on the field of research,” she added.

She said that it is possible that menstrual changes could be a result of stress, however, she says the vaccine could potentially impact the endometrium, or lining of the uterus.

“We don’t know because we haven’t looked – so few studies in females. I think that this is important as women are empowered to describe what is happening to them and hopefully more people will study it,” she said.

Galea said her own daughter had spotting just after getting her vaccination, but quickly forgot about it. As is the case with many who have experienced menstrual changes since the outset of the pandemic.

Another snag in determining the impact of the COVID-19 vaccine on menstrual cycles is that for researchers to find out, they’d have to re-do the vaccine clinical trials with menstruation as the focus.

“If you want to ask about menstrual cycles, you’d have to run the trial again with that as a primary outcome,” Galea said. “Certainly you could use it as a secondary thing to examine but I don’t think that many appear interested.”

All women of child-bearing age in the COVID-19 vaccine clinical trials were to take a form of birth control to prevent the risk of adverse effects on unborn children, according to each study’s qualifications. A long standing tradition for vaccine and drug trials, said Danska.

There is currently one study being conducted on menstrual changes after the COVID-19 vaccine. People who have received at least one dose of a vaccine, are 18 years of age or older, and have menstruated can participate.


It’s been well documented from the start of the pandemic that men seem to be worse off than women when it comes to severity of COVID-19 infections, and experts say hormones may be a key factor here.

A retrospective study in women receiving fertility assessments in Wuhan, China, who had previously tested positive for COVID-19, showed that those with longer menstrual cycles had more severe coronavirus symptoms. 

“The bottom line in that data, for me, is that it shows that those who were sickest have lengthened cycles, which means lower estrogen levels,” Prior said.

However, Prior noted that the study in Wuhan showed no changes to the AMH, a hormone secreted by ovarian follicles.

“The ovary isn't damaged by having COVID infection,” she said, adding that any menstrual changes as a result of getting COVID-19 are temporary.

“The changes that are occurring are adaptive and protective changes that are built into our system to protect us in times of stress,” Prior said.

Danska said it’s not uncommon for women to have stronger immune responses to vaccines, noting this has been well documented among women receiving the flu shot.

“What was generally observed is that women have a somewhat more robust response to a given amount of a vaccine, or immunogen as we would say,” said Danska.

Hormones are a key factor at play in the immune response, she says.

“Most of the thinking and, more importantly, most of the data look at this issue of hormone responses and it's not just the estrogen. It’s estrogen, it’s androgen… it's the whole complement of female hormones,” Danska said.

Despite this, she said female’s strong immune response should be viewed as a positive.

“These robust responses to vaccines are just one of many examples of the fact that women have better, have stronger immune responses to infection than men do,” said Danska.

For women who’ve heard that the day or two after inoculation are marked by not feeling well, she says to embrace this feeling.

“It's good… like, ‘Good on you, girl’… Your body's responding and you're going to protect yourself, and it reflects the potency of your immune response,” Danska said.