Emily R. Boniface from the Department of Obstetrics and Gynecology at Oregon Health & Science University recently spearheaded a study. Their analysis concluded that influenza vaccinations, provided individually or concurrently with COVID-19 vaccines, lead to small, temporary alterations in menstrual cycle length. Our research has shown that these changes are short-lived—on average less than one day.
The primary study analyses were conducted on 1,501 US participants aged 18-45 years old. Of note, all of them were users of a birth control app and non-hormonal contraception. Of the participants, 791 only received the influenza vaccine, while 710 received both the influenza and COVID-19 vaccines at the same time. The median age of our cohort was under 35 years, with 82% under the age of 35. In addition, 74.8% of study participants had at least a bachelor’s degree.
Findings from the Study
The influenza vaccination in isolation increased the menstrual cycle length by an average of 0.40 days. In comparison, those who received both vaccines saw a decrease of 0.49 days. This difference was not significant, p = .69. The scientists calculated that just 4.7% of people who got the influenza vaccine only would have had a cycle size change of eight days or extra. In comparison, only 5.9% of those who were up to date with both vaccines experienced this increase.
The cohort was heavily weighted towards those residing in the United States & Canada, at 62.5% of the sample. Nonetheless, racial and ethnic data were lacking for 72.2% of the participants with just 24.5% classified as White.
Impact of Vaccination Timing
The critical role of timing in vaccination to observe menstrual cycle changes. Vaccination during the follicular phase had the most pronounced effects. Cycle lengths increased by an average of 0.82 days for those who received only the influenza vaccine and by 0.99 days for those who received both vaccines.
These results suggest that vaccines lead to minor alterations in menstrual cycle characteristics. These changes aren’t drastic and aren’t permanent.
“In this cohort study of individuals with regular menstrual cycles, influenza vaccine given alone or in combination with a COVID-19 vaccine was associated with a small but temporary change in menstrual cycle length. These findings may help clinicians confirm the utility of vaccination for patients with concerns about menstrual adverse effects of vaccination,” – authors of the study
Implications for Future Research
Ultimately, the results of this study should come as good news for anyone nervous about experiencing possible menstrual irregularities in the wake of vaccination. Vaccinations are increasingly the linchpin of successful public health strategies. Leonard cautions that it’s important for doctors and patients alike to understand their impacts on bodily functions like menstrual cycles to build trust and adherence in patients.
Medical professionals can utilize this information to address any apprehensions that patients may have regarding vaccine-related side effects, particularly those related to reproductive health. We need to do more research to unpack these results. Only by investigating more populous, more racially and ethnically diverse populations can we confirm these findings and develop robust guidelines.
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