A significant number of people may experience period changes in the first two weeks after receiving the Covid-19 vaccine, suggests a new analysis of reports from over 35,000 people.
The research, published last week in the journal Science Advances, offers a comprehensive assessment of menstrual changes experienced by pre- and post-menopausal individuals following Covid vaccination.
“Doctors who weighed in on the subject after hearing early reports about post-vaccination menstrual changes were often dismissive of patients’ concerns,” study co-author Kathryn Clancy, a professor of anthropology at the University of Illinois Urbana-Champaign in the US, said in a statement.
Researchers believed these side effects could be tied to an uptick in immune-related inflammatory pathways following vaccination, and are less likely to be driven by hormonal changes.
They said such changes in menstruation are also sometimes seen following vaccination for typhoid, Hepatitis B and HPV.
“Menstruating and formerly menstruating people began sharing that they experienced unexpected bleeding after being administered a Covid-19 vaccine in early 2021,” noted scientists, including those from the University of Illinois at Urbana-Champaign.
“Because vaccine trials typically do not ask about menstrual cycles or bleeding, this side effect was largely ignored or dismissed,” they said.
Scientists suspect these changes associated with Covid vaccination are short term for most people and urgeed those who are worried to contact their doctors for further care.
“We want to reiterate that getting the vaccine is one of the best ways to prevent getting very sick with Covid, and we know that having Covid itself can lead not only to changes in periods, but also hospitalisation, long Covid and death,” said Katharine Lee, another author of the study from Tulane University in the US.
In the study, scientists analysed data from a survey to query people about their experiences after vaccination that was launched in April 2021.
While participants were surveyed for demographic and other information, the study focused on respondents’ reproductive history and experiences regarding menstrual bleeding.
In the analysis, only those who had not been diagnosed with Covid were included since Covid itself is sometimes associated with menstrual changes.
Researchers also excluded from the analysis data from people who were 45-55 years old to avoid confounding the results by including menstrual changes associated with perimenopause.
About 42 per cent of menstruating survey respondents reported a heavier menstrual flow after receiving the Covid vaccine.
While some experienced this in the first seven days, scientists said many other respondents reported changes 8-14 days after vaccination.
About 44 per cent reported no alteration of their menstrual flow after the vaccine, and a smaller percentage, 14 per cent, saw a mix of no change or lighter flow, the study noted.
Citing one of the limitations of the study, scientists said the analysis relied on self-reported experiences logged more than 14 days after vaccination, adding that it cannot establish causality or be seen as predictive of people in the general population.
However, they said it can point to likely associations between a person’s reproductive history, hormonal status, demographics and changes in menstruation following Covid vaccination.
Citing an example from the analysis, researchers said respondents who had experienced a pregnancy were most likely to report heavier bleeding after vaccination, with a slight increase among those who had not given birth.
They said a majority of non-menstruating premenopausal respondents on hormonal treatment experienced breakthrough bleeding after receiving the vaccine.
People who had experienced endometriosis, menorrhagia, fibroids or other reproductive problems were also more likely to report a heavier menstrual flow post-vaccination, scientists said.
“We’d love to see future vaccine testing protocols incorporate questions about menstruation that go beyond screening for pregnancy,” Dr Lee said.
“Menstruation is a regular process that responds to all kinds of immune and energetic stressors, and people notice changes to their bleeding patterns, yet we don’t tend to talk about it publicly,” she added.
