Are COVID-19 vaccines linked to heavier periods?

A lot of people have claimed they’ve had heavier periods, or unusual menstrual bleeding, after getting a COVID-19 vaccine – but there hasn’t yet been much clinical evidence for this.

Now, a study published in Science Advances hopes to add weight to the matter, reporting on a survey with nearly 40,000 participants. Among respondents with regular menstrual cycles, 42% reported heavier than normal bleeding following their vaccination.

“We suspect that for most people the changes associated with COVID-19 vaccination are short-term, and we encourage anyone who is worried to contact their doctor for further care,” says co-lead author Katharine Lee, a professor of anthropology at Tulane University, US.

“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.”

Read more: COVID-19 and women

The survey collected responses from 39,129 people who were currently menstruating, or had menstruated in the past. Among the 1815 respondents who weren’t menstruating because of hormonal treatments, 66% reported breakthrough bleeding after a COVID vaccination. Breakthrough bleeding was also reported by 66% of the 238 postmenopausal respondents.

“Unexpected breakthrough bleeding is one of the early signs of some cancers in post-menopausal people and in those who use gender-affirming hormones, so experiencing it can make people worry and require expensive and invasive cancer-screening procedures,” says Lee.

“This screening is very important so we can catch cancers early,” says co-lead author Kathryn Clancy, a professor of anthropology at the University of Illinois Urbana-Champaign, US. “Anyone with breakthrough bleeding should see their doctor. For diagnostic purposes, it would be helpful to know whether there are other causes for the bleeding.”

The researchers point out that, since the sample was self-selecting, their results can’t be considered representative of the whole population.

“While a very interesting paper because it is looking at something that anecdotally, many women reported after receiving COVID-19 vaccines, the inherent weaknesses in the study design make it difficult to attribute too much weight to the findings,” says Gino Pecoraro, an associate professor of obstetrics and gynaecology at the University of Queensland, who wasn’t involved in the research.

“The nature of the design using women referred to the website questionnaire after receiving social media or traditional media links raises significant selection biases and makes interpretation difficult and needing caution.”

Pecoraro reiterates, however, the paper’s point that menstruation usually isn’t recorded in clinical trials.

“It is very common for women’s periods to vary, particularly during stressful times and changes to a period after receipt of a vaccine has been documented many times over more than 100 years – so the phenomena is not new,” says Helen Petousis-Harris, an associate professor in the Department of General Practice and Primary Health Care at the University of Auckland, New Zealand, who also wasn’t involved in the research.

Read more: COVID-19 vaccination does not increase the risk of preterm birth

“With respect to COVID-19 vaccines, there are now several studies, using a variety of approaches, that suggest that in the month following receipt of a dose of COVID-19 vaccine, some women have a small change to their period.”

All of these recorded changes, according to Petousis-Harris, have been temporary.

“The important message is it is very clear that the vaccine has no adverse effects on fertility or pregnancy. There are many studies have looked at the effect of the vaccine on both male and female fertility and pregnancy.

“The evidence shows that getting the vaccine has no negative impact on any of these things and it is important for protecting pregnant women and their infants. These new findings are of no surprise and certainly no reason to delay or avoid a COVID-19 vaccine.”

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