Association Between Menstrual Cycle Length and Coronavirus Disease 2019 (COVID-19) Vaccination

Abstract

To assess whether coronavirus disease 2019 (COVID-19) vaccination is associated with changes in cycle or menses length in those receiving vaccination as compared with an unvaccinated cohort. METHODS:We analyzed prospectively tracked menstrual cycle data using the application "Natural Cycles." We included U.S. residents aged 18-45 years with normal cycle lengths (24-38 days) for three consecutive cycles before the first vaccine dose followed by vaccine-dose cycles (cycles 4-6) or, if unvaccinated, six cycles over a similar time period. We calculated the mean within-individual change in cycle and menses length (three prevaccine cycles vs first-and second-dose cycles in the vaccinated cohort, and the first three cycles vs cycles four and five in the unvaccinated cohort). We used mixed-effects models to estimate the adjusted difference in change in cycle and menses length between the vaccinated and unvaccinated cohorts. RESULTS:We included 3,959 individuals (vaccinated 2,403; unvaccinated 1,556). Most of the vaccinated cohort received the Pfizer-BioNTech vaccine (55%) (Moderna 35%, Johnson & Johnson/Janssen 7%). Overall, COVID-19 vaccine was associated with a less than 1-day change in cycle length for both vaccine-dose cycles compared with prevaccine cycles (first dose 0.71 day-increase, 98.75% CI 0.47-0.94; second dose 0.91, 98.75% CI 0.63-1.19); unvaccinated individuals saw no significant change compared with three baseline cycles (cycle four 0.07, 98.75% CI 20.22 to 0.35; cycle five 0.12, 98.75% CI 20.15 to 0.39). In adjusted models, the difference in See related editorial on page 479.

Effect of COVID-19 vaccination on menstrual periods in a prospectively recruited cohort

“…Although this finding was in line with that from a large and well-designed study carried out in the USA which also detected delays to the period following a dose of the vaccine [13], the delays we found were somewhat larger. We therefore considered the possibility that those participants who had returned their journals were more likely to have noticed any change than those who did not, inflating the postvaccination changes.…”

“…Importantly, periods returned to coming at the expected time in the interdose and post-vaccine cycles. These findings are in line with those from a recent study in the USA, which reported increases in cycle length associated with receiving either the second dose of vaccine, or both doses in the same cycle, but again noted that cycles rapidly returned to normal [13].…”

“…In response to similar reports to the USA's vaccine safety surveillance scheme, VAERS, the National Institutes of Health allocated $1.67m (£1.2m; C1.4m) for studies into a possible connection between COVID-19 vaccination and menstrual changes [12] and the first of these studies has recently reported [13]. The authors used prospectively logged data from a menstrual cycle tracking app: 3959 Americans logged at least six consecutive cycles; 2403 of them were vaccinated and 1556 acted as a control group.…”

Investigating trends in those who experience menstrual bleeding changes after SARS-CoV-2 vaccination

“…Overall, our results align with other recent studies which show significant menstrual cycle responsiveness to SARS-CoV-2 vaccination. For example, a Norwegian cohort study found increased reports of heavier periods and longer menstrual bleeding after vaccination which lasted for two to three months ( 86 ), and U.S.-based sample found longer cycle lengths after vaccination but no effect on bleeding duration ( 87 ). The only study published thus far which examined menstrual flow after vaccination had similar findings to ours, specifically that that people using hormonal contraceptives were more likely to experience heavier bleeding after vaccination; however, they did not find an association with diagnosed reproductive conditions although they note their sample size might be too small and underpowered for this analysis ( 88 ).…”

Web and social media searches highlight menstrual irregularities as a global concern in COVID-19 vaccinations

“…Antivaxxers later highlighted the worries regarding possible vaccine-induced menstrual irregularities, expanding unverified and often manipulative concerns, and promoting fears of vaccine– associated abortions and infertility 3,4 . Recent studies have examined the effects of COVID-19 disease 5 and vaccines 6,7 on menstrual irregularities, suggesting lack of adequate reporting of such irregularities due to women’s reluctance to discuss these matters with their physicians 8 . Yet whether these are anecdotal reports amplified by antivaxxers or a true uncharted association remains largely unknown.…”