
Investigators analyzing data on almost 2 million women participating in 17 studies observed a slight and transient increase in the length of menstruation after they received a COVID-19 vaccine, according to a study published late last week in PLOS One.
The authors said the study offers clarity on the topic. "Given the extensive reporting by the media on the topic, a continued lack of clarity can fuel further vaccine hesitancy, not just for COVID-19 vaccines but also more broadly with serious implication," they wrote.
Overall, women who received a COVID vaccine had a 19% greater risk of increase in menstrual cycle length as compared to unvaccinated women or women in pre-vaccination time periods (summary relative risk [sRR], 1.19; 95% confidence interval [CI], 1.11 to 1.26).
Changes observed in only 1 cycle
Both the Moderna and Pfizer mRNA vaccines carried the same 15% increased risk of an extended menstrual cycle. AstraZeneca and Johnson & Johnson had higher risks (sRR, 1.27 and 1.69, respectively).
After the first vaccine dose, menstrual cycle length increased an average of less than half of one day, and after the second dose 0.62 days. All changes were observed only in the first cycle after vaccination, and menstrual length returned to normal in the second cycle.
The fear of menstrual disturbance should not discourage anyone from getting COVID-19 vaccine.
"Results of this study show that there exists but a minimal and short-lasting risk of increased menstrual disturbance associated with COVID-19 vaccines that could likely be experienced by females as a normal variant sometime during a 12-month time-frame regardless of vaccination," the authors concluded. "The fear of menstrual disturbance should not discourage anyone from getting COVID-19 vaccine."