Although insufficient attention has been directed towards the effects of vaccination on menstrual experiences, a study published in Science Advances in September 2023 presents research into the link between COVID-19 vaccination and “unexpected vaginal bleeding” in “nonmenstruating women”. The study, carried out in Norway, examines self-reported data from 2021 after spontaneous reporting systems revealed an increase in “menstrual disturbances” and “post-menopausal bleeding” (PMB).  

Who was affected? 

The study involved almost 22,000 participants and examined three main areas: 

  1. Vaginal bleeding in postmenopausal women 
  2. Unexpected vaginal bleeding in perimenopausal women 
  3. Breakthrough bleeding in nonmenstruating premenopausal women 

The latter group involves a “substantial proportion of the female population” that does not menstruate because they use long-term hormonal contraception.  

“While an altered bleeding pattern after COVID-19 vaccination has been frequently addressed among menstruating women, few studies have investigated such experiences in women who do not menstruate due to hormonal contraception.”  

This figure (below) from the paper presents the data cleaning and inclusion process involved: 


What did the team find? 

Study author Kristine Blix told Nature that the results were “surprising”: 252 postmenopausal women, 1,008 perimenopausal women, and 924 premenopausal women report instances of unexpected vaginal bleeding. Of these experiences, around 50% were reported within 28 of vaccination. In postmenopausal women, the risk of vaginal bleeding “was increased two to threefold in the 4 weeks after vaccination”, compared to the pre-vaccination period. By comparison, the association with vaccination was “slightly stronger” in peri- and pre-menopausal women; the risk was increased three to fivefold. 

Blix states that the “most important contribution” of their research could be that “female bleeding patterns are included as end points, or monitored, in clinical trials of new vaccines”.  

Why this is important 

Dr Kate Clancy from the University of Illinois told Nature that unexpected bleeding after menopause is “often very concerning”, but this link could allow health providers to “put their bleeding incidence into context’. However, she’s “so glad” to see attention on a “very underserved group”. 

“Hooray for another group looking at peri- and postmenopausal people!” 

If this study is of interest do click here to see the full paper or subscribe for more vaccine safety insights. We look forward to hearing more discussions about vaccine safety at the Congress in Barcelona next month. Join us there!