Association between RNAm-Based COVID-19 Vaccines and Permanency of Menstrual Cycle Alterations in Spanish Women: A Cross-Sectional Study

SIMPLE SUMMARY: The purpose of this study was to delve more deeply into the medium and long-term relationship between mRNA-based vaccines and changes in menstrual pain, cycle length, and amount of bleeding in Spanish women. A total of 746 women (63% between 18–30 and 37% between 31–45 years old) participated in the study. Sixty-five per cent of the women perceived changes in their menstrual cycle after receiving the vaccines, irrespective of the type of vaccine or number of doses the novelty of the present study is that it confirms that menstrual cycle alterations in this sample could last more than 5 months after vaccination. ABSTRACT: Introduction: The purpose of this study was to delve more deeply into the medium and long-term relation between mRNA-based vaccines and changes in menstrual pain, cycle length, and amount of bleeding in Spanish women. Material and Methods: A total of 746 women (63% between 18–30 and 37% between 31–45 years old) participated in the study. A numerical rating scale was used for recording pain intensity, a pictorial chart for menstrual bleeding, and data from menstrual cycle duration, type of vaccine, number of doses and time from vaccination. Results: Sixty-five per cent of the women perceived changes in their menstrual cycle after receiving the vaccines, irrespective of type of vaccine or number of doses; all p values were >0.05. Most of them (n = 316 out of 484) reported more than one alteration in their menstrual cycle. Almost half of the participants had been vaccinated over 5 months (45%), 3–4 months (15%) 2–3 months (26%), and one month or less (13%) before. The percentage of women that reported alterations remained strongly constant across time, p > 0.05, ranging from 64 to 65%. Conclusions: Reported alterations in Spanish women after COVID vaccination remained more than 5 months after the last dose.