Increased Occurrence of Menstrual Disturbances in 18- to 30-Year-Old Women after COVID-19 Vaccination

Abstract

Background Many signals of menstrual disturbances as possible side effects of vaccination against COVID-19 have been reported. Our objective was to estimate the association between vaccination and the occurrence of such disturbances among women aged 18-30 in Norway.

Methods We used mobile-phone questionnaires to collect reports of menstrual disturbances from 5688 women aged 18-30 years, participating in the population-based Norwegian Young Adult Cohort. We estimated the relative risk of menstrual disturbances according to vaccination in a self-controlled case-series design, using the first six weeks after vaccination as the exposed period. We examined the occurrence of such disorders before and after both the first and second doses of vaccine. For subjects who had a menstrual disturbance after the first dose, we calculated the risk of recurrence after the second dose.

Findings The prevalence of any menstrual disturbance was 37.8% prior to vaccination. The relative risk of more heavy bleeding than usual during the exposed compared to unexposed period for first dose vaccination was 1.90 (95% CI: 1.69-2.13), while it was 1.84 (1.66-2.03) for the second dose. The proportion with menstrual disturbances in the most recent menstruation prior to the second vaccine dose was roughly the same as before the first vaccine dose. The risk of heavy bleeding after the second dose, given that it had occurred after the first, was 65.7%. We observed increased risks after vaccination also for other menstrual disturbances.

Interpretation Menstrual disturbances were generally common regardless of vaccination. We found a significant increase in menstrual disturbances after vaccination, particularly for heavier bleeding than usual, longer duration and for short interval between menstruations. Mechanisms underlying these findings may involve bleeding disturbances in general, as well as endocrine alterations.

Note:
Funding: The Norwegian Ministry of Health supported the study through a programme for corona vaccination surveillance.

Declaration of Interests: All authors are employees of the Norwegian Institute of Public Health

Ethics Approval Statement: The study has been approved by the Regional Ethics Committee for medical research, REK South-East A, no 229359. Date of approval Feb 19th 2021.

Keywords: Menstrual disturbances, cohort study, COVID-vaccine