Investigating trends in those who experience menstrual bleeding changes after SARS-CoV-2 vaccination

Abstract

Early in 2021, many people began sharing that they experienced unexpected menstrual bleeding after SARS-CoV-2 inoculation. We investigated this emerging phenomenon of changed menstrual bleeding patterns among a convenience sample of currently and formerly menstruating people using a web-based survey. In this sample, 42% of people with regular menstrual cycles bled more heavily than usual, while 44% reported no change after being vaccinated. Among respondents who typically do not menstruate, 71% of people on long-acting reversible contraceptives, 39% of people on gender-affirming hormones, and 66% of postmenopausal people reported breakthrough bleeding. We found that increased/breakthrough bleeding was significantly associated with age, systemic vaccine side effects (fever and/or fatigue), history of pregnancy or birth, and ethnicity. Generally, changes to menstrual bleeding are not uncommon or dangerous, yet attention to these experiences is necessary to build trust in medicine.

Fig. 1.. Flowchart of data cleaning and aggregation.

Note that totals in the yellow boxes do not add up to the numbers in the gray boxes due to uncertain menopause stage (n = 1522), currently or recently lactating (n = 2498), having had a hysterectomy (n = 43), discrepant responses (e.g., self-reported period details did not align with self-reported menstrual group), and the divisions made to the samples. Further details can be found in the Supplementary Materials. dx, diagnosis.

Fig. 2.. Descriptive statistics of the full sample (dose 1 displayed in solid bars and dose 2 displayed in striped bars).

The most salient vaccine and menstrual side effects pertaining to the analysis are presented here. The sample sizes of dose 2 variables decrease because of those who received the one-dose Johnson & Johnson vaccine. The respective samples become as follows: full, N = 35,660; age 18 to 24, N = 5698; age 25 to 34, N = 13,537; age 35 to 45, N = 11,970; age 46 to 54, N = 3898; age 55 to 80, N = 557.

Fig. 3.. Results of multivariate regressions.

Multivariate logistic regression of (A) heavier flow in the regularly menstruating group (N = 17,113, after removing those respondents with vaccines other than Pfizer or Moderna, or missing parity history or flow change) and (B) breakthrough bleeding in the nonmenstruating premenopausal group (N = 1771, after removing those respondents with vaccines other than Pfizer or Moderna, or missing parity history) after either dose of the vaccine. The graph presents the ratio of the odds of heavy bleeding occurring in the first group of the comparison versus the second group (except for age, which is in 10-year increments). If the odds ratio is greater than 1, the first group in the comparison has higher risk of experiencing heavier bleeding (or breakthrough bleeding). NH, not Hispanic/Latinx; CI, confidence interval.

Fig. 4.. Menstrual flow changes in regularly cycling individuals with diagnosed reproductive conditions.

Displayed on the x axis is the percentage of individuals reporting each flow change condition (y axis).

Fig. 5.. Breakthrough bleeding in nonmenstruating individuals.

Displayed on the x axis is the percentage of individuals reporting breakthrough bleeding after both doses, only following dose 2, only following dose 1, or no breakthrough bleeding during vaccination time (y axis).