French study finds that COVID-19 vaccination increases risk of heavy menstrual bleeding

Medical News: A recent nationwide case-control study in France has shed light on the potential link between COVID-19 mRNA vaccination and the risk of heavy menstrual bleeding in women. Conducted by researchers from various French institutions, including EPIPHARE Scientific Interest Group in Epidemiology of Health Products, the French National Agency for the Safety of Medicines and Health Products (ANSM), and the French National Health Insurance (CNAM), the study provides valuable insights into a health concern that has been inconsistently reported in previous research. This Medical News report explores the study findings, methodology, and its implications for public health.


French study finds that COVID-19 vaccination increases risk of heavy menstrual bleeding

Study Background and Purpose
The European Medicines Agency (EMA) had earlier considered abnormal menstrual bleeding as a potential side effect of COVID-19 mRNA vaccines, such as Comirnaty (Pfizer/BioNTech) and Spikevax (Moderna). Many women reported experiencing heavier-than-usual menstrual bleeding after receiving these vaccines. However, the link between the vaccines and menstrual irregularities, specifically heavy menstrual bleeding requiring hospital care, remained uncertain.
 
The French researchers aimed to address this gap in knowledge by assessing the risk of hospital care for heavy menstrual bleeding after COVID-19 vaccination, considering the number of doses and time since vaccination.
 
Methods and Study Design
This nationwide case-control study used data from the French National Health Data System, which includes information on healthcare use, socio-demographic characteristics, COVID-19 vaccinations, and hospital care. The study examined 4,610 women aged 15 to 50 years who were hospitalized for heavy menstrual bleeding between May 2021 and August 2022. These women, referred to as "cases," were compared to a control group of 89,375 women who had not been hospitalized for menstrual irregularities. The researchers matched the cases and controls based on factors such as age, place of residence, social deprivation index, and contraceptive use.
 
The study's primary focus was on determining the association between COVID-19 vaccination and heavy menstrual bleeding requiring hospital care. The researchers analyzed the risk based on the timing of the last vaccine dose and the type of vaccine received. Both primary vaccination (first and second doses) and booster doses were included in the analysis.
 
Key Findings: Increased Risk Within Three Months After Vaccination
The study found that women who had received a primary dose of the COVID-19 vaccine within the last 1 to 3 months were at a 20% higher risk of being hospitalized for heavy menstrual bleeding compared to unvaccinated women. The risk was especially pronounced among women living in socio-economically deprived areas and those who were not using hormonal contraception.
 
Interestingly, no increased risk was observed within the f irst month after vaccination or beyond three months. Additionally, booster doses did not appear to elevate the risk of heavy menstrual bleeding.
 
In practical terms, the study estimated that approximately 103 cases of heavy menstrual bleeding requiring hospital care in France could be attributed to COVID-19 vaccination during the study period. Given that over 13 million women in France were vaccinated between May 2021 and August 2022, the overall risk remains relatively low. However, for the women affected, the experience was significant enough to require hospital care.
 
Implications for Public Health and Vaccine Safety
These findings provide important context for ongoing discussions about COVID-19 vaccine safety, particularly in relation to women's health. While the study confirms a modest increase in the risk of heavy menstrual bleeding after primary vaccination, it also underscores that the overall incidence remains low. Moreover, the increased risk appears to be short-lived, confined to the three-month period following vaccination.
 
From a public health perspective, this study reinforces the importance of monitoring vaccine side effects, especially those that may disproportionately affect specific populations, such as women in socio-economically disadvantaged areas. Health professionals should be aware of these findings to provide appropriate care and reassurance to women who experience abnormal menstrual bleeding after vaccination.
 
Understanding the Biological Mechanism
The biological mechanism behind the association between COVID-19 vaccination and menstrual disturbances remains unclear. Researchers have proposed several hypotheses, including the involvement of the hypothalamic-pituitary-ovarian axis and immune-mediated changes that could affect menstrual bleeding. Some experts suggest that immune changes triggered by the vaccine may lead to temporary disruptions in menstrual cycles, similar to the way other vaccines can cause menstrual irregularities.
 
While this study focused on mRNA vaccines, similar menstrual side effects have been reported with other vaccines, such as the human papillomavirus (HPV) vaccine and hepatitis B vaccine. Understanding the underlying mechanisms may help researchers develop strategies to mitigate these side effects in future vaccination campaigns.
 
Study Limitations and Strengths
As with any study, there are limitations to consider. One of the primary limitations of this research is its reliance on hospital data. While the study captured the most severe cases of heavy menstrual bleeding that required hospital care, it may have missed less severe cases that were managed in outpatient settings. This limitation could result in an underestimation of the true incidence of post-vaccination menstrual disturbances. Additionally, the study was limited to women aged 15 to 50 years, so its findings may not apply to other age groups, such as post-menopausal women.
 
Despite these limitations, the study has several strengths. The use of nationwide data and a large sample size enhances the reliability of the findings. Furthermore, the researchers adjusted for numerous potential confounding factors, including socio-demographic characteristics, healthcare use, and comorbidities, which helps to isolate the effect of COVID-19 vaccination on heavy menstrual bleeding.
 
Conclusion: A Modest but Manageable Risk
In conclusion, this study provides valuable evidence of an increased risk of heavy menstrual bleeding within three months of primary COVID-19 vaccination with mRNA vaccines. However, the risk is modest and appears to be temporary, with no increased risk observed beyond three months. For women who experience heavy menstrual bleeding after vaccination, the findings suggest that the condition is likely to resolve over time. Importantly, the study highlights the need for continued monitoring of vaccine side effects, particularly those that affect women's reproductive health.
 
The study findings were published in the peer-reviewed journal Vaccine.
https://www.sciencedirect.com/science/article/pii/S0264410X24009344
 
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https://www.thailandmedical.news/news/the-impact-of-postmenopausal-medications-on-covid-19-progression-in-women