Association between menstrual cycle length and vaccination against coronavirus disease 2019 (COVID-19)
For one study, researchers looked to see if vaccination against coronavirus disease 2019 (COVID-19) caused changes in a cycle or menstrual length compared to an unvaccinated control group. Using the “Natural Cycles” program, they evaluated prospectively collected menstrual cycle data. They recruited people aged 18 to 45 in the United States with typical cycle lengths (24 to 38 days) for 3 consecutive cycles before the first dose of vaccination, followed by cycles of vaccine doses (cycles 4 to 6 ) or, if they are not vaccinated, 6 cycles over a comparable duration. Mean intra-individual variation in menstrual cycle and duration was calculated (three pre-vaccination cycles versus cycles of first and second doses in the vaccinated cohort, and the first three cycles versus cycles four and five in the unvaccinated cohort). vaccinated). The adjusted difference in cycle change and menstrual length between vaccinated and unvaccinated cohorts was estimated using mixed-effects models.
They enlisted 3,959 people (vaccinated 2,403; unvaccinated 1,556). The Pfizer-BioNTech vaccine was administered to the majority of the immunized population (55%) (Moderna 35%, Johnson & Johnson/Janssen 7%). Overall, the COVID-19 vaccine was associated with less than a day increase in cycle length for both cycles of vaccine doses compared to pre-vaccine cycles (first dose 0.71 day d increase, 98.75% CI 0.47-0.94; second dose 0.91, 98.75% CI 0.63-1.19); unvaccinated individuals saw no significant difference from three baseline cycles (cycle four 0.07, 98.75% CI 0.22 to 0.35; cycle five 0.12, 98.75 CI % -0.15 to 0.39). The difference in cycle length between the vaccinated and unvaccinated groups was less than 1 day in the adjusted models for both doses (difference in variation: first dose 0.64 days, 98.75% CI 0.27-1, 01; second dose 0.79 days, 98.75% CI 0.40-1.18). Vaccination had no effect on menstrual cycle length. Immunization against coronavirus disease 2019 (COVID-19) has been linked to a slight change in cycle length but not menstrual length.