A new study has found that Covid-19 vaccines lead to menstrual irregularities in half of the women who received the vaccine.
The survey, published in the journal Science Advances on Friday, was conducted by researchers from the University of Illinois and the University of Washington School of Medicine. In April 2021, about 40,000 people aged 18 to 80 from around the world were asked to fill out an online questionnaire about menstrual cycles, and scientists later analyzed and systematized the answers.
The researchers say they launched the study after a large number of anecdotal reports since early 2021 describing unusual menstrual bleeding in transgender women and men who received the Covid-19 vaccine.
According to the results of the study, 42% of respondents who previously had regular cycles reported heavy bleeding after receiving an injection. Meanwhile, 44% did not notice any change, and 14% reported that they had lighter periods.
In addition, other participants who do not normally menstruate, including transgender men, postmenopausal women, and those taking long-acting birth control, also experienced unusual bleeding.
Respondents received Pfizer, Moderna, and Johnson & Johnson vaccines or other vaccines approved outside the United States. Participants also revealed that none of them contracted Covid-19 prior to being vaccinated.
The study — the largest of its kind to date — appears to confirm the findings of earlier, smaller studies.
However, the researchers note that the changes seen in women’s cycles are temporary and should in no way be used to cast doubt on the overall efficacy and safety of Covid vaccines.
The researchers concluded that the potential consequences of contracting the virus are likely to be more serious than menstrual problems, while warning that delaying vaccination even by a few weeks is not a good idea for women.
They said they hope more transparency about the side effects of Covid-19 vaccines will help reduce people’s hesitation and fear.