Covid-19 vaccination and menstrual cycle length in the Apple Women's Health Study

Elizabeth A Gibson; Huichu Li; Victoria Fruh; Malaika Gabra; Gowtham Asokan; Anne Marie Z Jukic; Donna D Baird; Christine L Curry; Tyler Fischer-Colbrie; Jukka-Pekka Onnela; Michelle A Williams; Russ Hauser; Brent A Coull; Shruthi Mahalingaiah

doi:10.1038/s41746-022-00711-9

Covid-19 vaccination and menstrual cycle length in the Apple Women's Health Study

NPJ Digit Med. 2022 Nov 2;5(1):165. doi: 10.1038/s41746-022-00711-9.

Authors

Affiliations

¹ Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
² Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
³ Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, Durham, NC, USA.
⁴ Health, Apple Inc., Cupertino, CA, USA.
⁵ Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
⁶ Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA. shruthi@hsph.harvard.edu.

^# Contributed equally.

Abstract

COVID-19 vaccination may be associated with change in menstrual cycle length following vaccination. We estimated covariate-adjusted differences in mean cycle length (MCL), measured in days, between pre-vaccination cycles, vaccination cycles, and post-vaccination cycles within vaccinated participants who met eligibility criteria in the Apple Women's Health Study, a longitudinal mobile-application-based cohort of people in the U.S. with manually logged menstrual cycles. A total of 9652 participants (8486 vaccinated; 1166 unvaccinated) contributed 128,094 cycles (median = 10 cycles per participant; inter-quartile range: 4-22). Fifty-five percent of vaccinated participants received Pfizer-BioNTech's mRNA vaccine, 37% received Moderna's mRNA vaccine, and 8% received the Johnson & Johnson/Janssen (J&J) vaccine. COVID-19 vaccination was associated with a small increase in MCL for cycles in which participants received the first dose (0.50 days, 95% CI: 0.22, 0.78) and cycles in which participants received the second dose (0.39 days, 95% CI: 0.11, 0.67) of mRNA vaccines compared with pre-vaccination cycles. Cycles in which the single dose of J&J was administered were, on average, 1.26 days longer (95% CI: 0.45, 2.07) than pre-vaccination cycles. Post-vaccination cycles returned to average pre-vaccination length. Estimated follicular phase vaccination was associated with increased MCL in cycles in which participants received the first dose (0.97 days, 95% CI: 0.53, 1.42) or the second dose (1.43 days, 95% CI: 1.06, 1.80) of mRNA vaccines or the J&J dose (2.27 days, 95% CI: 1.04, 3.50), compared with pre-vaccination cycles. Menstrual cycle change following COVID-19 vaccination appears small and temporary and should not discourage individuals from becoming vaccinated.