Menstrual abnormalities after COVID-19 vaccination in the Netherlands

Based on spontaneously reporting data and a prospective cohort event monitoring (CEM) study an incidence of menstrual disorders of 41.4 per 1000 women aged 54 years or younger was observed. Amenorrhoea/oligomenorrhoea and heavy menstrual bleeding collectively accounted for about half of all abnormalities reported.

Over 24.000 spontaneous reports received at The Netherlands Pharmacovigilance Centre Lareb and over 500 episodes of menstrual abnormalities (among 16.929 included women) were analyzed in the CEM study.

Significant associations were observed for the age group 25–34 years (odds ratio 2.18; 95% confidence interval 1.45–3.41) and the Pfizer vaccine (odds ratio 3.04; 95% confidence interval 2.36–3.93). No association was observed for body mass index and presence of most comorbidities assessed. The use of hormonal contraceptives was not consistently associated with the occurrence of menstrual abnormalities.

In 2022, The European Medicines Agency recommended heavy menstrual bleeding to be added to the product information of the COVID-19 vaccines of Moderna and Pfizer as an adverse reaction with unknown frequency. Further studies are needed to elucidate the mechanism of these adverse reactions.

Read the full paper in the British Journal of Clinical Pharmacology here.