New study shows Covid vaccines do disrupt menstrual cycles

Covid vaccines do disrupt menstrual cycles
Photo by CDC on Unsplash

A newly released study has shown that the Covid-19 vaccines do disrupt menstrual cycles, as previous anecdotal evidence had suggested. The findings, published in the journal Obstetrics & Gynaecology, validate claims from thousands of women who reported erratic changes in their cycle after getting the shot.

The study was led by a team of scientists from Oregon Health and Science University after they analysed nearly 4,000 women and their cycles through a fertility tracking app. Of the women in the study, some were vaccinated and some were unvaccinated. The first vaccine dose caused an average increase of 0.64 days or 15.36 hours. There then was shown an average increase of 0.79 days or roughly 18.98 hours following the second dose.

However, a subgroup of app users who received two vaccine doses in the same menstrual cycle (358 users) had a larger average increase in cycle length of two days, reports The Daily Mail. The findings are preliminary as the study is set to run for a whole year to gather more data.


The research was announced in September 2021 and is being funded by a $1.67 million grant from the National Institutes of Health (NIH). It involves five universities that aim to determine whether or not Covid vaccines do disrupt menstrual cycles. The universities include Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University and Oregon Health and Science University.

Diana W. Bianchi, M.D., director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), said in a statement: “It is reassuring that the study found only a small, temporary menstrual change in women.

“These results provide, for the first time, an opportunity to counsel women about what to expect from COVID-19 vaccination so they can plan accordingly.”

The study is just a smaller part of the year-long research that came about when thousands of women in the US and UK reported erratic menstrual cycles. On September 2, 35,000 British women came forward saying their periods were disrupted after getting a COVID vaccine. No fertility issues were uncovered at the time, according to an analysis of the data by Dr Victoria Male, a lecturer in reproductive immunology at Imperial College London.

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