An international research team led by Oregon Health & Science University has discovered a slight yet notable association between vaccination and menstrual cycle changes. The study, published in JAMA Network Open, reveals that individuals who received the influenza vaccine—alone or in conjunction with a COVID-19 vaccine—experienced a temporary increase in menstrual cycle length, specifically when vaccinated during the follicular phase.
The research analyzed data from 1,501 individuals, aged 18 to 45, who tracked their menstrual cycles through a digital birth control application prior to vaccination. Participants had average cycle lengths ranging from 24 to 38 days and were not utilizing hormonal contraception. Of the cohort, 791 received the influenza vaccine alone while 710 were administered both vaccines on the same day.
Using a within-person control design, the study calculated the change in menstrual cycle length relative to the three pre-vaccination cycles. The findings highlighted an adjusted mean increase of 0.40 days for those vaccinated with only the influenza vaccine, and 0.49 days for those receiving both vaccines. Notably, these changes were statistically insignificant, with p-values (0.69, 0.46, and 0.28) indicating no meaningful difference between the two groups.
Despite the minor increases, the study emphasized that these changes were temporary. Both groups returned to their pre-vaccination cycle lengths in the subsequent cycle, suggesting that the effect of vaccination on menstrual cycles is not lasting. Additionally, only 4.7% of individuals who received the influenza vaccine alone and 5.9% who received both vaccines reported clinically meaningful changes, defined as an increase of eight days or more.
The researchers also found that the timing of the vaccination within the menstrual cycle significantly influenced the outcomes. Those vaccinated during the follicular phase experienced an adjusted mean increase of 0.82 days with the influenza vaccine alone and 0.99 days with both vaccines. In contrast, individuals vaccinated during the luteal phase saw no significant change.
“These findings confirm that concurrent administration of the influenza vaccine and COVID-19 vaccine does not appear to significantly increase the risk of menstrual disturbances,” stated the researchers. They noted that public concern regarding the impact of vaccinations on menstrual health and fertility is supported by evidence of only minor and temporary alterations in cycle length.
The study reassures individuals that understanding the timing of vaccination can help mitigate concerns surrounding menstrual cycle changes. Furthermore, it invites further investigation into how immune responses to vaccines may affect menstrual health.
As vaccination efforts continue globally amid various public health challenges, this research contributes essential insights into women’s health, aiming to inform both clinicians and patients about potential vaccine-related effects on menstrual cycles. The intricate relationship between vaccinations and menstrual health continues to warrant examination, emphasizing the importance of inclusive study designs in future clinical research.
-Rashmi Kumari
