Do mRNA COVID-19 vaccines cause heavy menstrual bleeding?

Health Canada has examined the link between vaccination with monovalent mRNA COVID-19 vaccines (Comirnaty–Pfizer-BioNTech or Spikevax–Moderna) and the risk of heavy menstrual bleeding. Heavy menstrual bleeding patterns include menorrhagia (heavy cyclic vaginal bleeding with blood loss of > 80 mL per cycle), menometrorrhagia (heavy irregular vaginal bleeding) and polymenorrhagia (heavy prolonged cycles consistently lasting > 8 days).1 The review included only monovalent mRNA vaccines (Comirnaty and Spikevax), as data were limited for the bivalent vaccines (Comirnaty Original & Omicron BA.4/BA.5, Spikevax Bivalent [Original/Omicron BA.1], and Spikevax Bivalent Original/Omicron BA.4/5) at the time of the review.1 Health Canada's review included data from clinical trials, Canadian and international postmarketing reports and scientific literature. The review did not find any scientific or medical evidence to indicate that vaccination with monovalent mRNA vaccines increases the risk of heavy menstrual bleeding.1 Health Canada concluded that Canadian product safety information for Comirnaty and Spikevax accurately reflects the current evidence and no updates to the Canadian product monographs for Comirnaty or Spikevax regarding heavy menstrual bleeding are required.1 On October 28, 2022, the Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency (EMA) recommended that heavy menstrual bleeding be added to product information for Comirnaty and Spikevax, as a side effect of unknown frequency. The PRAC came to this conclusion after reviewing cases reported during clinical trials, cases spontaneously reported to the EMA adverse reactions database and findings from the medical literature.2 The PRAC concluded that there is “at least a reasonable possibility” that heavy menstrual bleeding is causally associated with these COVID-19 vaccines. However, the PRAC acknowledged that most cases of heavy menstrual bleeding were nonserious, temporary in nature and have no effect on reproduction and fertility.2 Therefore, the possibility of developing heavy menstrual bleeding should not discourage patients from vaccination. A recent meta-analysis of 16 epidemiological studies found that menorrhagia, oligomenorrhea (infrequent menstrual periods) and polymenorrhea (menstrual periods at intervals of < 21 days) were the most common menstrual irregularities after COVID-19 vaccination. However, the authors concluded that further studies are needed to confirm whether there is a causal relationship between COVID-19 vaccination and menstrual irregularities.3 Another recent study found an increased risk of menstrual disturbances after COVID-19 vaccination, particularly heavier bleeding than usual, prolonged bleeding, a shorter interval between menstruations, and stronger period pain.4 However, an additional study found no strong associations between COVID-19 vaccination and menstrual cycle regularity, bleeding duration, heaviness of bleed or menstrual pain.5 To provide clarity on this issue, menstrual characteristics should be included in future COVID-19 vaccine trials.4 In addition, Health Canada encourages healthcare professionals to continue to report adverse reactions suspected of being associated with COVID-19 vaccines.1 References 1. Government of Canada. Safety brief. mRNA COVID-19 vaccines (Comirnaty and Spikevax) and the risk of heavy menstrual bleeding. Health Product InfoWatch: July 2023. (accessed August 1, 2023). 2. European Medicines Agency. Meeting highlights from the Pharmacovigilance Risk Assessment Committee (PRAC) 24-27 October 2022. October 28, 2022. Comirnaty and Spikevax: heavy menstrual bleeding added as a side effect. (accessed August 1, 2023). 3. Al Kadri HM, Al Sudairy AA, Alangari AS, et al. COVID-19 vaccination and menstrual disorders among women: findings from a meta-analysis study. J Infect Public Health 2023;16(5):697-704. (accessed August 1, 2023). 4. Trogstad L, Laake I, Robertson AH, et al. Heavy bleeding and other menstrual disturbances in young women after COVID-19 vaccination. Vaccine 2023;S0264-410X(23)00801-0. Published online July 3, 2023. (accessed August 1, 2023). 5. Wesselink AK, Lovett SM, Weinberg J, et al. COVID-19 vaccination and menstrual cycle characteristics: A prospective cohort study. Vaccine 2023;41(29):4327-34. Published online June 5, 2023. (accessed August 1, 2023).

Do mRNA COVID-19 vaccines cause heavy menstrual bleeding?

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