When COVID-19 vaccines became widely available, some women reported changes in the timing and length of their menstrual cycles after getting vaccinated.
Now, nearly two years later, a global study has confirmed that COVID-19 vaccination can lead to temporary changes in cycle length for some people.
Study participants who were vaccinated reported, on average, a nearly one-day day increase in the length of their menstrual cycle length after receiving their first COVID vaccine shot, and a half-day increase after receiving their second dose.
Getting vaccinated produces a strong immune system response in the days following the shot, which may cause temporary changes to menstrual cycles.
Studies have also documented temporary menstrual cycle changes among women who get COVID-19 infections.