The study’s survey of over 9,600 participants found that, on average, a dose of vaccine was associated with an increase in menstrual cycle length of about half a day. Cycle length returned to the pre-vaccination average in the following cycle.
“Our preliminary insights … emphasize that menstrual cycle changes associated with COVID-19 vaccination are small and temporary and should not discourage people from getting vaccinated,” according to an update on the Apple Women’s Health Study website.
Research collaborators on the Apple Women’s Health Study include Harvard T.H. Chan School of Public Health, the National Institute of Environmental Health Sciences (NIEHS), and Apple.
Read the update about the study: COVID-19 vaccines and menstrual cycles