COVID-19 vaccines linked to heavier periods in some recipients, survey finds

person with hot water bottle lying in pajamas

The changes are likely to be caused by inflammatory pathways rather than disruption of ovarian hormones. Image Credit: Monkey Business Images/

Thousands of people have reported unusually heavy menstrual bleeding after receiving a COVID-19 vaccine, according to a new study published in the journal Science Advances. The sample includes postmenopausal and transgender people who have menstruated before but currently do not expect to menstruate at all – although the authors point out that there is no reason to assume that these changes in short term pose a health risk.

The sudden recurrence of menstrual bleeding in those who no longer usually have periods is called breakthrough bleeding and can be distressing for many reasons. For example, it can be a sign of uterine cancer, and those who experience this side effect after vaccination are therefore likely to worry unnecessarily.

According to the researchers, studies that highlight the prevalence of this phenomenon are needed to alleviate these fears and combat misinformation about the effects of COVID-19 vaccines on fertility and general health. “In general, changes in menstrual bleeding are neither uncommon nor dangerous, but attention to these experiences is necessary to build confidence in medicine,” they write.

The study presents the results of a social media survey, in which people over the age of 18 were asked to describe the impact of vaccination on their menstrual habits. Conducted between April and October 2021, the survey attracted over 165,000 responses, of which 39,129 were analysed.

Overall, 42% of participants reported having had heavier periods than usual after receiving a vaccine, and 44% described no change in menstrual flow. These findings are important because vaccine safety clinical trials do not typically monitor menstruation and only consider symptoms that appear within a week of vaccination, although many survey respondents reported menstrual changes. over seven days after a sting.

A more detailed breakdown of the data revealed that heavier bleeding was more common among people of Hispanic or Latino descent, as well as those who had previously been pregnant or were diagnosed with a reproductive problem such as endometriosis, menorrhagia or polycystic ovary syndrome.

“Among respondents who usually do not menstruate, 71% of people on long-acting reversible contraceptives, 39% of people on gender-affirming hormones, and 66% of people in menopause reported breakthrough bleeding” , report the authors.

Although the mechanism linking COVID-19 vaccines to unusual menstrual phenomena is unclear, researchers believe the cause is more likely to involve inflammatory pathways than ovarian hormonal disruption.

This hypothesis is supported by the fact that those who took hormonal contraception were just as likely to have heavy periods as spontaneous menstruation, indicating that the whole process is not related to hormone levels.

Importantly, this study did not include a control group and likely drew responses primarily from those who experienced troubling side effects. As such, the results may not be representative of the general population and are likely to disproportionately highlight the experiences of those who have noticed heavy or unexpected bleeding after vaccination.

Due to these limitations, the authors would like to emphasize that they “cannot estimate prevalence or incidence based on our methodological approach to this emerging phenomenon, and the associations reported here cannot establish causation.”

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