"Abstract
Background: Many signals of menstrual disturbances as possible side effects of vaccination against COVID-19 have been reported. Our objective was to compare the risk of menstrual disturbances before and after vaccination among women aged 18–30 years in Oslo, Norway.
Introduction
Previously unforeseen signals of menstrual disturbances as possible side effects of the COVID-19 vaccines have been reported to spontaneous reporting systems in many countries, including Norway. By 23 November 2022, the UK Yellow Card system had received more than 50 000 reports of menstrual disorders including heavier than usual periods, delayed periods and unexpected vaginal bleeding, after COVID-19 vaccination.
To date, a number of studies have been conducted to evaluate the potential association between COVID-19 vaccination and menstrual disturbances. Many studies report menstrual disturbances at high frequencies after vaccination, and interval changes have been more commonly observed among vaccinated individuals by use of data from cycle tracking applications... Preliminary analyses from the current study were... considered important evidence in the safety assessment conducted by the Pharmacovigilance Assessment Committee (PRAC) for the European Medicines Agency (EMA). In a statement issued in October 2022, PRAC concluded that there is at least a reasonable possibility of a causal association between COVID-19 vaccination and heavy menstrual bleeding. They recommended that heavy menstrual bleeding should be included in the product information of the mRNA vaccines as a possible side effect...
Results ...
3.2. Self-controlled case series analyses
We observed increased risk of heavier menstrual bleeding than usual after both the first and second vaccine dose, RR = 1.90 (95 % CI 1.69–2.13) and RR = 1.84 (95 % CI 1.66–2.03), respectively (Table 3). Increased risks after both the first and second dose were also seen for prolonged bleeding (RR = 1.46 (95 % CI 1.31–1.61) for dose 1 and 1.71 (95 % CI 1.55–1.89) for dose 2); shorter interval (RR = 1.32 (95 % CI 1.19–1.46) for dose 1 and 1.57 (95 % CI 1.42–1.73) for dose 2); and stronger period pain (RR = 1.35 (95 % CI 1.24–1.47) for dose 1 and 1.62 (95 % CI 1.49–1.77) for dose 2)."
© 2023 The Authors. Published by Elsevier Ltd.
This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.