Dr. Alison Edelman, a professor of obstetrics and gynecology at Oregon Health and Science University, led a new scientific study at Oregon Health and Science University (OHSU) demonstrating that vaccination can cause changes to the timing of menstruation. A survey conducted by anthropologists found numerous reports of unusually heavy flows and even breakthrough bleeding among some people who hadn’t menstruated in years. However, the results of the study also show the effects are temporary. 

The Findings

Edelman’s team took data from a popular app known as “Natural Cycles,” which people can use to track their menstrual cycles. Looking at data from 3,959 individuals, they were able to see a small shift in the time between bleeding.

“We see a less-than-one-day change in their menstrual cycle length with vaccination,” Edelman says.

In other words, people who were vaccinated experienced — on average — a slightly longer menstrual cycle around the time of their first and second doses.


This work was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development

The Research Institution 

OHSU is Oregon’s only public academic health center. They are a system of hospitals and clinics across Oregon and southwest Washington. They are also an institution of higher learning, with schools of medicine, nursing, pharmacy, dentistry, and public health – and with a network of campuses and partners throughout Oregon. They are a national research hub, with thousands of scientists developing lifesaving therapies and deeper understanding, as well as a statewide economic engine and Portland’s largest employer. As a public organization, they provide services for the most vulnerable Oregonians, and outreach to improve health in communities across the state.

Lead Researcher/Investigator

Dr. Alison Edelman, a professor of obstetrics and gynecology at Oregon Health and Science University

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