Nurse giving patient a shot in the arm.

mRNA Vaccines: Risk for Heavy Menstrual Bleeding

Cases of menstrual disorders, particularly unusually heavy menstrual bleeding, have been reported following RNA vaccination against COVID-19.

In France, this safety signal has been confirmed and added to the product characteristics summaries and vaccine leaflets for mRNA vaccines in October 2022. However, few studies have accurately measured this risk to date.

To address this gap in research, the French scientific interest group in the epidemiology of health products, ANSM-Cnam EPI-PHARE, conducted a study to assess the risk for heavy menstrual bleeding requiring hospitalization after COVID-19 vaccination in France.

"This study provides new evidence supporting the existence of an increased risk for heavy menstrual bleeding following COVID-19 vaccination with mRNA vaccines," wrote the authors.

Study Details

The study included all women aged 15-50 years who were diagnosed with heavy menstrual bleeding in the hospital between May 12, 2021, and August 31, 2022. Participants were identified in the National Health Data System, and the study population totaled 4610 women.


Each participant was randomly matched with as many as 30 women who had not been hospitalized for abnormal genital bleeding and had similar characteristics in terms of age, department of residence, social deprivation index of the commune of residence, and contraceptive method.

Women who had a recent pregnancy, hysterectomy, or coagulation disorder within the specified time frames were excluded.

At the time of the study, 71% of cases and 70% of controls had received at least one dose of the COVID-19 vaccine. Among vaccinated participants, 68% and 66%, respectively, received a vaccination dose (first or second dose). An mRNA vaccine (Comirnaty or Spikevax) was the last vaccine for 99.8% of the population.

Increased Risk 

Compared with control women, those hospitalized for heavy menstrual bleeding were more likely to have received their last dose of mRNA vaccine (Comirnaty or Spikevax) in the previous 1-3 months. This association was observed for vaccination doses (odds ratio [OR], 1.20), indicating a 20% increased risk, but it was not found for booster doses (OR, 1.07).

This association was particularly notable for women residing in socially disadvantaged communities (OR, 1.28) and women not using hormonal contraception (OR, 1.28).

The risk did not appear to be increased beyond 3 months after vaccination. Researchers noted that the increased risk may have occurred earlier, considering the likely interval between initial symptoms and hospitalization.

Assuming a causal relationship, the estimated number of cases attributable to vaccination was 8 cases per million vaccinated women, totaling 103 cases among all women aged 15-50 years who were vaccinated in France between May 12, 2021, and August 31, 2022.

As of the study date and in the 3 years before the study, none of the authors had any conflicts of interest with pharmaceutical companies. 

This article was translated from the Medscape French edition.

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