Early in 2022, a study funded by the U.S. National Institutes of Health (NIH) found women receiving one dose of a COVID-19 vaccine during a single menstrual cycle had an increase in cycle length of nearly one day.
Recently, a large international study funded by the NIH confirmed those findings linking COVID-19 vaccination with an average increase in menstrual cycle length of less than one day.
For most study participants, the increase resolved in the cycle following vaccination.
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