New study: COVID shots affect women menstrual cycles
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Not long after the rollout of coronavirus vaccines last year, women around the country began posting on social media about what they believed was a strange side effect: changes to their periods.
Now, new research shows that nearly 20,000 people are representing over 250,000 cycles, who recorded their data using the app Natural Cycles between October 1, 2020 and November 7, 2021. For the vaccinated cohort, they looked at three prevaccine cycles and at least the first Covid-19 vaccine dose cycle. For the unvaccinated, they included four to six cycles from a similar time period.
The participants came from a number of countries, but mostly from Europe and the US and Canada. Nearly two-thirds of the 15,000 vaccinated participants had received the Pfizer/BioNTech vaccine, although participants had also received the Johnson & Johnson, Moderna and Oxford-AstraZeneca vaccines among others.
The data, published Tuesday in the British Medical Journal, was taken from a popular period tracking app called Natural Cycles and included people from around the world, but most were from North America, Britain and Europe. The researchers used “de-identified” data from the app to compare menstrual cycles among 14,936 participants who were vaccinated and 4,686 who were not.
There was also a “significant increase” noted in the rate of respondents who had a more than eight-day increase in their cycle length, the authors said, finding 13.5% of the vaccinated individuals and 5% of the unvaccinated participants reporting this.
“These findings provide additional information for counseling women on what to expect after vaccination,” said Dr. Diana Bianchi, director of the National Institute of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), in a news release. “Changes following vaccination appear to be small, within the normal range of variation, and temporary.”
“We found no differences in menses length in any group of vaccinated individuals, compared with the unvaccinated cohort,” the study says.
Researchers don’t know exactly why the vaccines seem to affect menstrual cycles, but Alison Edelman, a professor of obstetrics and gynecology at Oregon Health & Science University, who led the study, said that the immune and reproductive systems are linked and that inflammation or a strong immune response could trigger menstrual fluctuation.
Any change in getting your period can be stressful, triggering worries about an unplanned pregnancy or a health scare, and people have expressed frustration that public health officials didn’t warn them about a possible side effect or do more research before rolling out the vaccines.
The research does have some limitations, the authors say, including that people using hormonal birth control were not participants, the researchers were limited in the number of post vaccine cycles and they were unable to account for the effects of potential infections in participants.