A sober survey of more than 35.000 women ensures that vaccination against Covid-19 has some side effect on menstruation. This is the report that offers the most complete evaluation to date on the menstrual changes experienced by pre- and postmenopausal people during the first two weeks after receiving the Covid-19 vaccine.
Many women have reported problems with their menstruation after being vaccinated, said University of Illinois Urbana-Champaign scientists who led the study.
But, because menstrual cycles or bleeding are not typically asked about in vaccine trials, this side effect is largely ignored or dismissed.
Initially, patient concerns were ignored, acknowledges Kathryn Clancy, coordinator of the work.
However, other vaccines, such as those for typhoid, hepatitis B and HPV, are sometimes associated with changes in menstruation, Clancy says.
These side effects are thought to be linked to an increase in immune-related inflammatory pathways and are likely due to hormonal changes.
These side effects are linked to increased inflammatory pathways
"We suspect that, for most people, the changes associated with the Covid-19 vaccine are short-term, and we encourage anyone who is concerned to contact their doctor for further care," says another of the authors. of the report, Katharine Lee, who nevertheless stresses that it is necessary to "reiterate that getting vaccinated is one of the best ways to prevent Covid disease, and we know that having Covid itself can lead not only to changes in menstruation, but also to hospitalization, prolonged Covid and even death ”.
The researchers used a survey to ask women about their experiences after vaccination. The survey, launched in April 2021, in addition to requesting demographic and other information, focuses on the reproductive history of the surveys and also experiences in relation to menstrual bleeding.
The team downloaded the survey data on June 29, 2021. Only people who had been diagnosed with Covid-19 were included in the analysis, as Covid-19 itself is sometimes associated with menstrual changes.
The study also excludes women between the ages of 45 and 55 to avoid confounding the results by including menstrual cycles associated with perimenopause.
“We focused our analysis on those women who menstruate regularly and those who don't currently menstruate but have in the past,” says Clancy. "This latter group includes postmenopausal women and those receiving hormonal therapies that suppress menstruation, for whom bleeding is especially surprising."
A statistical analysis revealed that 42,1% of menstruating respondents reported heavier menstrual flow due to receiving the Covid-19 vaccine. Some experienced it within the first seven days, but many others saw changes between 8 and 14 days after vaccination. About the same proportion, 43,6%, reported that their menstrual flow was unchanged after the vaccine, and a smaller percentage, 14,3%, experienced a mixture of no change or lighter flow, they report. the researchers.
Because the study was based on self-reported experiences recorded more than 14 days after vaccination, it was unable to establish causality and was not considered predictive of people in the general population, Lee says.
But it can point to possible associations between a person's reproductive history, hormonal status, demographics, and changes in menstruation after vaccination against Covid-19.
For example, the analysis revealed that investigations that had experienced pregnancy were the most likely to report heavier bleeding after vaccination, with a slight increase among those who had not given birth. Most non-menopausal premenopausal women surveyed who followed hormonal treatment experienced intermittent bleeding after receiving the vaccine. More than 70% of respondents using long-acting reversible contraception and 38.5% of those undergoing gender-affirming hormone treatments reported this side effect.
It would be desirable that future vaccine testing protocols incorporate questions about menstruation
Although increased menstrual flow in some people can be transient and rapid, unexpected changes in menstruation can be cause for concern, Lee says.
"Unexpected intermittent bleeding is one of the earliest signs of some cancers in postmenopausal people and those using gender hormones, so experiencing it can raise concerns and require costly and invasive cancer screening," Lee explained.
The researcher concludes that it would be necessary for "future vaccine testing protocols to incorporate questions about menstruation that go beyond pregnancy detection."
The study has been published in “Science Advances”.
