A study released in March 2023 in iScience suggests that COVID-19 infection was a greater factor than COVID-19 vaccination in observed changes to a patient’s menstrual cycle. The researchers identified “substantial public concern” related to “disruption of menstrual cycles”. However, the possible causes, such as vaccination, infection, pandemic-related stress, or lifestyle changes, remain “understudied”. Therefore, it is imperative that further investigation is carried out to gain the relevant knowledge for “advising women about the relative risk of experiencing menstrual disturbance when getting vaccinated against COVID-19 versus infected”.  

Vaccines and menstruation 

The authors suggest that prior to the pandemic, research into the relationship between vaccination and menstrual cycle health was limited to prophylactic typhoid, HPV, and hepatitis B vaccines. Since the pandemic and associated vaccination drive, prospective studies have found changes in cycle length for participants. Beyond cycle length, other studies have identified “various changes in regularity, duration, and volume”.  

“While there is accumulating evidence that COVID-19 vaccination-related menstrual symptoms are associated with small and temporary changes in cycle length, there has been no quantitative assessment of the risk factors for menstrual disturbances following COVID-19 vaccination prior to widespread media attention.”  

The paper contrasts the “emerging picture” of a “small effect of COVID-19 vaccine on cycle length” with research into the associations between infection and menstrual cycle changes. This is described as “scarce and inconsistent”.  

“A study better powered to evaluate the independent association of SARS-CoV-2 and abnormal cycle changes is better needed to inform vaccination decisions.”  

What does the study find? 

Based on data collected in the UK “prior to widespread media attention” the study identified that “perceived menstrual cycle changes” after vaccination are “very common” in the context of “international pharmacovigilance standards” (over 10%). Specifically, these perceived changes are “increased for participants reporting a history of COVID-19 disease”, but “decreased among those who use combined contraceptives”.  

Furthermore, the authors conclude that “vaccination alone does not lead to abnormal cycle parameters”, but COVID-19 is associated with an “increased risk” of reporting frequent cycles, prolonged periods, heavier flows, and more inter-menstrual bleeding. They acknowledge that the experiences of cycle changes after vaccination are “diverse”. 

Facts and figures of the study 

The study involved almost 5,000 vaccinated pre-menopausal participants, and the University of Edinburgh describes a “vast majority” of 82% who reported “no menstrual changes”. 6.2% reported “more disruption”, 1.6% reported “less disruption”, and 10.2% reported “other changes”

It is notable that of the 18% who reported changes, the risk was higher among those who smoked, had previously had COVID-19, or who were not using oestradiol-containing contraceptives. The authors then considered a wider population of 12,000 participants, which included participants who had not been vaccinated against COVID-19 as well as vaccinated participants.  

“Vaccination alone did not show increased abnormal menstrual cycle factors.”  

Is this enough? 

The authors recognise that their study is limited, particularly in its reliance on people recalling previous menstrual experiences. Dr Jackie Maybin from the University of Edinburgh identifies a potential for “bias” in those who chose to complete the study. 

“Nevertheless, our results are reassuring that COVID-19 vaccination does not cause concerning menstrual changes, and helpful for identifying people who might be at higher risk of experiencing menstrual disturbance.” 

Did you observe menstrual changes following COVID-19 vaccination, or has this research encouraged you in the context of widespread media concern?  Join us at the World Vaccine Congress next month to discuss COVID-19 vaccination with experts across the community.