A new study has shown that many of the complaints about the effects of coronavirus vaccines on periods were valid. Twenty-nine thousand people around the world were studied on a wide range of factors and compared with those who hadn’t been vaccinated. The results showed that people who received the vaccination experienced an average delay in getting their periods by 1 day compared with those who hadn’t been vaccinated.
The study published in the British Medical Journal Tuesday reports on data from a popular period-tracking app called Natural Cycles, which includes women from around the world. Most of the participants were from North America, Britain, and Europe; researchers analyzed 14,936 cycles among those who received the vaccine and 4686 cycles among those who did not. Because users tracked their menstrual cycles every month on the app—which included information about contraceptive use and other factors—researchers were able to analyze three menstrual cycles before vaccination and at least one cycle after. They compared these results with four cycles in unvaccinated participants.
A study led by Alison Edelman, a professor of obstetrics and gynecology at Oregon Health & Science University, found that women who received the HPV vaccine experienced an increase in the length of their menstrual cycle after the first dose. However, those who received two vaccinations within one menstrual cycle experienced greater disruptions. In this group, the average increase in cycle length was four days, and 13 percent experienced a delay of eight days or more; 5 percent in the control group did not experience any side effects.
Research has shown that vaccines can have a variety of effects on periods. A survey published last fall collected information from 160,000 people—including transgender and postmenopausal people—and found that thousands reported heavier bleeding than usual or breakthrough bleeding.
The study did not address all of the questions raised by people about vaccines and periods, including how the shots affect trans men and nonbinary individuals. Since the vaccines were rolled out, many people on social media have complained of longer, heavier and more-painful periods after getting vaccinated. However, this study did show that, on average, getting vaccinated does not appear to cause longer periods.
