The effect of BNT162b2 SARS‐CoV‐2 mRNA vaccine on menstrual cycle symptoms in healthy women

Objective To investigate the impact of the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) mRNA BNT162b2 vaccine on women's menstrual cycle. Methods In this questionnaire‐based cross‐sectional study, we assessed menstrual pattern and changes in women who completed the SARS‐CoV‐2 mRNA BNT162b2 vaccine 3 months before and after receiving the vaccine. Included were women aged 18–50 years without known gynecologic comorbidities who regularly monitor their menstruation through electronic calendars. All participants competed a detailed questionnaire on their menstrual symptoms including information on any irregular bleeding. To minimize bias, each woman served as a self‐control before and after vaccination. Primary outcome was rate of irregular bleeding following vaccination and secondary outcome was presence of any menstrual change, including irregular bleeding, mood changes, or dysmenorrhea following the vaccine. Results A total of 219 women met the inclusion critieria. Of them, 51 (23.3%) experienced irregular bleeding following the vaccine. Almost 40% (n = 83) of study participants reported any menstrual change following vaccination. Parity was positively asssociated with irregular bleeding with 26 (50%) of those suffering from irregular bleeding being multiparous compared with only 53 (31.5%) of women with no irregular bleeding (nulliparous 46% vs 60%, multiparous 50% vs 31%, rest 4% vs 8%, P = 0.049). The presence of medical comorbidities was also significantly higher among patients who experienced irregular bleeding (20.0% vs 6.0%, P = 0.003). Conclusion Our study shows relatively high rates of irregular bleeding and menstrual changes after receiving the SARS‐CoV‐2 mRNA BNT162b2 vaccine. Further research is needed to confirm our findings and to better characterize the magnitude of change and any possible long‐term implications. Synopsis Significant rates of menstrual changes including irregular bleeding were found following the BNT162b2 SARS‐CoV‐2 mRNA vaccination.