Prevalence of and risk factors for self-reported menstrual changes following COVID-19 vaccination: a Danish cohort study.

STUDY QUESTION: Are there some characteristics that render individuals more susceptible to report menstrual changes following the Coronavirus disease 2019 (COVID-19) vaccination? SUMMARY ANSWER: We found that 30% of menstruating women reported menstrual changes following COVID-19 vaccination and several potential risk factors including stress, vaccine concerns, severe COVID-19 infection, and immediate vaccine symptoms were associated with these reports. WHAT IS KNOWN ALREADY: Studies suggest that COVID-19 vaccination might temporarily prolong menstrual cycle length by less than 1 day. Specific characteristics may trigger menstrual changes in temporal relation to the vaccination simply by chance or render women more vigilant to potential menstrual changes after being vaccinated. However, research investigating potential risk factors for reporting menstrual changes following COVID-19 vaccination is limited. STUDY DESIGN, SIZE, DURATION: A population-based Danish cohort study. Data were collected from May 2021 to December 2021 as a part of the BiCoVac Cohort with the aim of examining non-specific effects following COVID-19 vaccination. The main study population included 13 648 menstruating women aged 16-65 years who completed all surveys, received their first dose of a COVID-19 vaccine during the data collection period, and completed questions related to their menstrual cycle. PARTICIPANTS/MATERIALS, SETTING, METHODS: Potential risk factors included 14 biological, physical, or psychological measures. Information on most potential risk factors was self-reported and collected before the participants' first COVID-19 vaccination. Information about any menstrual change following COVID-19 vaccination was self-reported at the end of the data collection period. Logistic regression analyses were used to estimate crude and adjusted odds ratios (ORs) with 95% CIs for the association between each potential risk factor and reporting menstrual changes following COVID-19 vaccination. MAIN RESULTS AND THE ROLE OF CHANCE: Any menstrual change following COVID-19 vaccination was reported by 30% of menstruating women. Most of the potential risk factors were associated with reports of menstrual changes following COVID-19 vaccination. In particular, higher odds were found among women who reported ≥5 immediate vaccine symptoms; OR 1.67 [1.50-1.86], had had a prior severe COVID-19 infection; OR 2.17 [1.40-3.35], had a high-stress level at baseline; OR 1.67 [1.32-2.10], or were concerned about COVID-19 vaccines prior to vaccination; OR 1.92 [1.50-2.45]. Lower odds were found among women with regular menstrual cycles using hormonal contraception; OR 0.71 [0.65-0.78]. LIMITATIONS, REASONS FOR CAUTION: We were unable to address the causal effect of COVID-19 vaccination on the reported menstrual changes, as information about menstrual changes was not available among non-vaccinated women. WIDER IMPLICATIONS OF THE FINDINGS: The study identified several potential risk factors for reporting menstrual changes following COVID-19 vaccination. Further studies are needed to establish causal associations and the clinical impact of self-reported menstrual changes. STUDY FUNDING/COMPETING INTEREST(S): The BiCoVac data collection was funded by TrygFonden (id-number: 153678). No competing interests are declared. TRIAL REGISTRATION NUMBER: N/A.

Immediate adverse reactions following COVID-19 vaccination among 16-65-year-old Danish citizens.

INTRODUCTION: There is sparse knowledge of immediate adverse reactions following COVID-19 vaccination. OBJECTIVE: This study aimed to estimate the frequency and number of immediate adverse reactions following COVID-19 vaccination in a Danish population. METHODS: The study used data from the Danish population-based cohort study BiCoVac. The frequencies of 20 self-reported adverse reactions were estimated for each vaccine dose stratified by sex, age, and vaccine type. Also, the distributions of number of adverse reactions following each dose were estimated stratified by sex, age, vaccine type, and prior COVID-19 infection. RESULTS: A total of 889,503 citizens were invited and 171,008 (19 %) vaccinated individuals were included in the analysis. The most frequently reported adverse reaction following the first dose of COVID-19 vaccine was redness and/or pain at the injection site (20 %) while following the second and third dose, tiredness was the most frequently reported adverse reaction (22 % and 14 %, respectively). Individuals aged 26-35 years, females, and those with a prior COVID-19 infection were more likely to report adverse reactions compared with older individuals, males, and those with no prior COVID-19 infection, respectively. Following the first dose, individuals vaccinated with ChAdOx1-2 (AstraZeneca) reported more adverse reactions compared with individuals vaccinated with other vaccine types. Individuals vaccinated with mRNA-1273 (Moderna) reported more adverse reactions following the second and third dose compared with individuals vaccinated with BNT162b2 (Pfizer-BioNTech). CONCLUSION: The frequency of immediate adverse reactions was highest among females and younger persons, however, most of the Danish citizens did not experience immediate adverse reactions following COVID-19 vaccination.