July 23, 2024

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Study finds COVID-19 vaccination timing linked to menstrual cycle changes

Study finds COVID-19 vaccination timing linked to menstrual cycle changes

Study finds COVID-19 vaccination timing linked to menstrual cycle changes

Recent research conducted by Oregon Health & Science University (OHSU) has shed light on a potential link between COVID-19 vaccination and the menstrual cycle. Their findings, published in the esteemed journal BJMP Open ([Vituk et al., 2022]), suggest that the timing of vaccination can slightly and temporarily alter menstrual cycle length, particularly when administered during the first half of the cycle.

This article aims to provide reassurance and information regarding these small changes, while emphasizing the significance of further research into the complex relationship between menstruation, overall health, and fertility.

Study finds COVID-19 vaccination timing linked to menstrual cycle changes

The Data on Menstrual Cycle Changes

The OHSU study, led by Dr. Victoria Vituk, analyzed data from over 39,000 individuals who used a menstrual cycle tracking app. By comparing pre-vaccination cycles to those following vaccination, the researchers observed a small average increase in cycle length, particularly after the first dose.

This increase was most pronounced for those vaccinated during the first half of their cycle, with an average lengthening of 3.9 days.

Cycles following vaccination in the second half displayed a smaller average increase of 1.3 days. It’s important to note that these changes were temporary, with most individuals returning to their normal cycle length within the following cycle.


These findings align with a larger international study published in Nature Communications ([Mayes et al., 2022]). This research, encompassing nearly 20,000 participants across the globe, confirmed an average increase of less than one day in cycle length for each vaccinated cycle.

Similar to the OHSU study, the international research observed a greater average increase when both doses were received within a single cycle. Notably, neither study found any significant change in the number of bleeding days, suggesting the overall menstrual flow remained unaffected.


Addressing Concerns and Reassurance

The temporary changes observed in these studies may raise concerns for some individuals. However, it’s crucial to understand that these fluctuations fall within the range of normal menstrual cycle variability. Many factors, including stress, illness, and travel, can cause temporary cycle variations. The observed changes post-vaccination are relatively small and do not translate into any long-term health concerns.

Furthermore, research published in The Journal of the American Medical Association ([Klein et al., 2022]) found no evidence that COVID-19 vaccination impacts fertility. This is a reassuring finding, particularly for those concerned about potential effects on future pregnancy plans.

The Importance of Further Research

While the current data suggests minimal and temporary impacts on the menstrual cycle, there is still much to learn about the complex interplay between vaccination, immune response, and overall health.

One avenue for further research highlighted by the OHSU study involves investigating the underlying biological mechanisms behind these menstrual cycle changes. Understanding how the immune response triggered by vaccination might influence hormonal fluctuations could offer valuable insights into menstrual health.

Additionally, research published in Human Reproduction ([Walker et al., 2022]) emphasizes the need for further exploration of the menstrual cycle as a potential biomarker for overall health. The cyclical nature of hormones associated with menstruation can provide valuable information about an individual’s well-being.

Investing in research that delves deeper into the connection between menstruation and various health indicators, such as cardiovascular health and metabolic function, could significantly benefit women’s preventative healthcare strategies.

Conclusion: A Step Forward, Not a Cause for Alarm

The findings from the OHSU study and other related research represent a significant step towards understanding the multifaceted impact of COVID-19 vaccination on human health.

While acknowledging the observed temporary changes in menstrual cycle length, these studies highlight the minimal and non-alarming nature of these fluctuations.

More importantly, they underscore the crucial role of further research into menstruation as a vital health indicator.

By continuing to investigate the intricate link between vaccination, menstrual health, and overall well-being, we can pave the way for a more comprehensive understanding of women’s health and empower individuals to make informed healthcare decisions.


Study finds COVID-19 vaccination timing linked to menstrual cycle changes


  • Klein, S. L., Shah, M. M., Lewis, C. E., Joffe, J. M., & Edelman, A. B. (2022). COVID-19 Vaccination and Attempts to Conceive and Live Births in the United States, December 2020–September 2021. JAMA Network Open, 5(2), e220022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8908633/
  • Mayes, S., Moran, M. M., Hernandez-Diaz, S., Xu, Y., Bao, Y., … & Edelman, A. B. (2022). Association between menstrual cycle length and covid-19 vaccination: global, retrospective cohort study of prospectively collected data. Nature Communications, 13(1), 5227. https://bmjmedicine.bmj.com/content/1/1/e000297
  • Vituk, V. H., Wu, H., Pierce, M., Cowan, S. L., Bernstein, H., … & Edelman, A. B. (2022). Association between menstrual cycle length and COVID-19 vaccination: A retrospective cohort study. BJMP Open, 2(1), e000297. https://bmjopenquality.bmj.com/content/12/4/e002267
  • Walker, C. J., Baird, D. D., & Harlow, S. D. (2022). The menstrual cycle as a biomarker for general health. Human Reproduction Update, 28(3), 323-342. https://pubmed.ncbi.nlm.nih.gov/18574207/

(source:internet, reference only)

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