COVID-19 vaccine and Menstrual conditions in female: data analysis of the Vaccine Adverse Event Reporting System

Background: In reports of adverse reactions following vaccination with the coronavirus disease 2019(COVID-19) vaccines, there have been fewer reports of concern for menstrual disorders in female. Objective: Our study used Vaccine Adverse Event Reporting System(VAERS)to investigate and analyze the relationship between COVID-19 Vaccines and menstrual disorders in female. Methods: We collected reports of menstrual disorders in VAERS from July 2, 1990 to November 12, 2021, and performed a strati�ed analysis. The potential relationship between COVID-19 vaccine and reports of menstrual disorders was evaluated using the Reporting Odds Ratio (ROR) method. Results: A total of 14,431 reports of menstrual disorders were included in the study, and 13,118 were associated with COVID-19 vaccine. The ROR was 7.83 (95% con�dence interval [95%CI]:7.39-8.28). The most commonly reported event was Menstruation irregular (4998 reports), and a higher percentage of female aged 30-49 years reported menstrual disorders (42.55%) after exposure to COVID-19 Vaccines. Both for all reports of menstrual disorders (ROR=5.82; 95%CI:4.93-6.95) and excluding reports of unknown age (ROR=13.02; 95%CI:10.89-15.56), suggest that female age may be associated with menstrual disorders after vaccination with the COVID-19 Vaccines. Conclusion: Our study suggests a potential safety signal among female who received the COVID-19 vaccine, which may cause menstrual disorders in young adult female (30-49 years old). However, due to the well-known limitations of spontaneous reporting data, it is challenging to directly de�ne menstrual disorders as an adverse event of the COVID-19 Vaccines, and reports of adverse


Background
Coronavirus disease of 2019 [1] (COVID-19) is a highly pathogenic viral infection caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).COVID-19 infection remains a global concern since the end of 2019 to date.According to WHO, as of January 6, 2022, 293,750,692 cases of COVID-19 have been diagnosed worldwide, and 55,972,114 cases have been diagnosed in the United States.For epidemic control, the safe and effective vaccine is the long-term solution to control the COVID-19 global pandemic [2] .Research studies [3] have shown that an average vaccination level of about 80 doses per 100 inhabitants between countries can sustain a reduction in the number of con rmed cases and deaths.The recent emergence of the Omicron variant further emphasizes the importance of vaccination, and prevention efforts needed to protect against COVID-19.
The FDA approved three COVID-19 vaccines for emergency use in the United States in mid-December 2020 [4,5] and late February 2021 [6] , respectively.By the end of 2021, more than a dozen COVID-19 vaccines in six categories are approved for use worldwide.Local and systemic reactions were the predominant types of adverse events observed in pre-emergency authorization clinical trials of these vaccines.Because of the short development cycle of COVID-19 vaccines, there are continuing concerns about the post-marketing safety and e cacy of vaccines.In order to continue to monitor the postmarketing safety of vaccines, countries around the world have taken different measures to collect information about vaccine recipients.The Centers for Disease Control and Prevention in the United States uses the Vaccine Adverse Reaction Reporting System VAERS for ongoing monitoring of the safety of the COVID-19 vaccine [7] .
Since the launch of the COVID-19 vaccine, more research points have focused on special groups such as the elderly [8] , adolescents [9,10] , and maternity [11,12] .More attention is paid to aspects such as rare allergic reactions [13] and cardiovascular system diseases [14] after vaccination, and less attention is paid to female's menstrual conditions.The purpose of this study is to discuss the safety of COVID-19 vaccines in female based on real data spontaneously reported in the VAERS and to attempt to analyze the potential relationship between COVID-19 vaccines and trends in reporting of menstrual disorders.

Aim of the study
The purpose of this study was to detect signals of menstrual disorder-like adverse reactions after COVID-2019 vaccination using the US Vaccine Adverse Event Reporting System (VAERS) database.

Database
Established in 1990, VAERS [15] (https://vaers.hhs.gov/) is a system for spontaneous and voluntary reporting of any suspected adverse drug reactions (ADRs) associated with vaccine use, jointly administered by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA).The primary purpose of VAERS is to detect early signals and generate hypotheses about possible new vaccine adverse events that were not identi ed in premarketing trials.VAERS accepts reports from vaccine recipients, parents, health care providers, vaccine manufacturers, and others.The VAERS report form collects information about the individual who received the vaccine, the type number of vaccine received, and the adverse reaction itself.
Signs and symptoms of adverse reaction are coded using the Medical Dictionary of Regulatory Activities (MedDRA) [16] .A single VAERS report can contain multiple MedDRA preferred terms.The following reports are categorized as "serious" reports under the US Code of Federal Regulations [17] :Hospitalization, Prolonged hospitalization, Emergency room visits, Disability, Life-threatening, or Death.

Dataset
After removing sensitive patient information, the original data les were downloaded from the VAERS website in comma-separated value (CSV) format.We downloaded the dataset in VAERS from the 1990 build through November 12, 2021, both U.S. regions and non-U.S.regions.The dataset consists of three separate data les for data, vaccines, and symptoms.

Data Selection
Use navicat15 for data mining.The following strategy was used:(1) Exclude all reports of male and unknown gender.Search for the following MedDRA preferred terms: "Menstruation irregular" "Menstruation delayed" "Menstrual disorder" "Hypomenorrhoea" "Menorrhagia" "Intermenstrual bleeding" "Metrorrhagia" "Amenorrhoea" (2) Each report was reviewed to clarify that the menstrual disorders were not caused by pregnancy (3) The ID, type of vaccine injected, and dose of injection were checked for each report, and reports with multiple repetitions of the same ID were excluded.(4) We extracted information on ID, vaccine type, vaccine dose, age, type of menstrual disorder, patient outcome, vaccination date, reporting interval, and past history from each report.Detailed interpretation of the reports can be found in the VAERS Data Use Guide [18] .

Data Analysis
The integration, extraction, and ltering of the reported data are performed by navicat15, and the description and statistical analysis of the data are realized by Free Statistics software version 1.4.
We summarized the basic characteristics of the reports by different types of menstrual disorders, age, reporting interval, severity, and past history, and performed a strati ed analysis of age and reporting interval.Characterization of the types of menstrual disorders reported for different vaccine types, statistical analysis using Fisher's exact test.A line graph is used to indicate the trend in the type of report.
The Reporting Odds Ratio (ROR) [19] was used to assess the disproportionate reporting of adverse reactions, with the lower limit of the ROR 95% con dence interval [95%CI] > 1 and a number of reports ≥ 3 suggesting the generation of an adverse signal.We performed the following sensitivity analyses of menstrual disorders events: (1) US and non-US regions; (2) strati cation by age; and (3) exclusion of cases of unknown age.
VAERS is a self-reporting vaccine adverse reaction surveillance system that meets the de nition of a study as speci ed in 45 CFR 46 [20] .Exemptions (2018Requirements).It is not subject to Institutional Review Board review and informed consent requirements.

Reports of Menstrual disorders in Vaccine Adverse Event Reporting System (VAERS)
Figure 1 shows the report selection process, including the reasons for exclusion.By November 12, 2021, 1742590 cases of adverse events were recorded in the VAERS database, and 60.94% of them were female.The category including menstrual disorders events 14,331 reports (1.36%), of which 13,118 (90.90%) were exposed to COVID19 vaccine and 13,13 (9.10%) were exposed to another vaccine.There were 1047452 (98.64%) other adverse events, 587325 (56.07%) were exposed to COVID-19 vaccine and 460130 (43.93%) were exposed to other vaccines.The reported species of serious adverse events were mainly related to Death, Life-threatening, Emergency room visits, Hospitalized, Prolonged hospitalization, and Disability.There were no reports of deaths in the COVID-19 vaccine group, and a total of 1079 serious adverse events were reported (8.22%).901 serious adverse events (68.62%) were reported in the non-COVID-19 vaccine group, three deaths were reported which were the result of exposure to Human papillomavirus vaccine(2 reports)and Hepatitis B virus vaccine(1 report).More than one-third of the reports in both groups mentioned a prescription or nonprescription drugs that the vaccine recipient was taking at the time of vaccination and 1175 cases (8.20%) were suffering from a disease, while 6481 cases (45.22%) had been diagnosed with a disease prior to vaccination.Comparison between groups revealed that the distribution of reports of menstrual disorders by age group was heterogeneous (p < 0.001).Except for the type of vaccine that could not be speci ed, the remaining three groups reported signi cantly higher proportions in the 30-39 age group than in other age groups, respectively accounting for 19.53%, 38.54%, and 31.67% of the total.The dose distribution by injected vaccine was also heterogeneous (P < 0.001), with Dose 1 being reported at a signi cantly higher rate than Dose 2 and Dose 3.Only 1596 cases (16.60%) of vaccine recipients recovered from the adverse event when the adverse reaction information was reported, and 66.33% did not recover at the time of reporting.Multiple MedRDA terms can exist in one adverse reaction report, so the sum of the individual events ofmenstrual disorders events may be greater than the total number of reports.

Reporting Odds Ratio
Reporting Odds Ratio analysis of reported events for the COVID-19 vaccine show as Table3 to Table6.The distribution of adverse events according to type (Menstrual disorder vs. other adverse reactions) and vaccination status (COVID-19 vaccines vs. other vaccines) is reported in Table 3. ROR estimated to be 7.83 (95% CI:7.39-8.28),suggests that COVID-19 vaccine may be a risk sign for the occurrence of events related to menstrual disorders.To further verify the correlation, three sensitivity analysis of the ROR were also performed.Firstly grouped by region of adverse reaction reporting (US vs. non-US) and vaccination status, ROR was 0.78(95% CI:0.70-0.88),suggested that the reports of menstrual disorders after vaccination with the COVID-19 vaccine are not related to the regional distribution.Secondly grouped by age and type of report, compared the reported rates of adverse events associated with menstrual disorders in the 30-49 age group with those in other age groups, ROR was 5.78(95% CI:4.86-6.88).Finally, excluding reports of unknown age, ROR was 12.46(95% CI:10.41-14.92).Suggests that age may be a risk ag for the event of menstrual disorders after vaccination with the COVID-19 vaccine.

Discussion
Coronavirus disease 2019 (COVID-19) is as an emerging infectious disease (EID) that has caused the worst public health catastrophe of the 21st century thus far.In order to contain the spread of the epidemic, countries around the world have launched vaccination campaigns for COVID-19 vaccine and have taken various measures to monitor for adverse reactions after vaccination.VAERS as a vaccine adverse reaction self-reporting system, a total of 14,431 menstrual disorder-like events were reported by female in VAERS, and 13,118 (90.90%) were exposed to the COVID-19 vaccine, from the establishment of the database in 1990 to November 12, 2021.The general characteristics of the reports showed that female in the age group 30-49 years reported the highest number of incidents of menstrual disorders compared to other vaccines.There were 1065 reports mentioning serious adverse events, again with the highest percentage of reports for P zer-Biontech vaccination.The majority of reports of menstrual disorders occurred after the rst dose of the COVID-19 vaccine, with only about 0.5% reported after the third dose of the vaccine.The time between vaccination and adverse reaction reporting was within 100 days in 82.92% of patients, but only 18.01% of patients reported that their adverse reactions had disappeared, and 62.88% of patients reported that they still had adverse reactions related to vaccination.
To my knowledge, this is the rst time that a menstrual disorder-related event has been linked to the COVID-19 vaccine.Normal female menstruation is judged by the cycle of menstruation, the period, the volume, the color, the quality and the accompanying symptoms of menstruation.Among the events of menstrual disorders reported by the COVID-19 vaccine, Menstruation irregular was found to be the most frequently reported, followed by Menstruation prolonged, Intermenstrual bleeding and Menstrual disorder, with Menorrhagia being the least frequently reported.Dietary nutrition, environmental factors, lifestyle and mental health conditions are important factors affecting menstrual irregularities in female of reproductive age [21] .During the covid-19 epidemic, female were more vulnerable to stress and were signi cantly more depressed and distressed than men [22] , and middle-aged females are the major groups for the rst vaccination.This may explain the climb in reports of menstrual disorders after vaccination with the COVID-19 vaccine.Our study found a potential association signal between COVID-19 vaccine and menstrual disorders events with ROR = 7.83 and met the lower limit of ROR 95% CI > 1 and number of cases > 3.However, adverse reactions were reported independent of region, with ROR < 1.In addition, studies [23] have found a greater correlation between prolonged and irregular menstrual cycles and the risk of premature death (age < 70 years), so that menstrual disorders in female must be taken seriously enough.
Study shows age and gender differences in adults who report adverse reactions after vaccination with COVID-19 vaccine.However, after the launch of COVID-19 vaccine, attention to adverse reactions associated with vaccination has been focused on the elderly [8] , adolescents [9] , and even pregnant female and young children [24] , while attention to young adult female has been lacking.However, female of reproductive age account for the majority of adverse reaction reports received by VAERS for menstrual disorders.Our study found that reports of adverse reactions to menstrual disorders in females aged 30-49 years increased nearly tenfold compared to the pre-marketing period of the vaccine.There was a danger signal between this age group of female compared to other age groups for menstrual disorders events after COVID-19 vaccination with a lower limit of the ROR 95% CI > 1.To address some limitations of the spontaneous data, such as missing data in the report, a sensitivity analysis was conducted to exclude age unknowns and produce similar results.Reports of menstrual disorder-like events after vaccination of female with the COVID-19 vaccine are age-related, and females of reproductive age between 30-49 years old need to pay particular attention to adverse reactions after vaccination.
Three COVID-19 vaccines are authorized or approved for use among adults in the United States, respectively: mRNA-1273 from Moderna [5] BNT162b2 from P zer-BioNTech [4] Ad26.COV2 from Janssen [6] .Inoculation with P zer-BioNTech accounted for the majority of reports of menstrual disorders, with Moderna in second place and Janssen in third.As of November 2, 2021, approximately 248 million doses of the P zer-BioNTech COVID-19 vaccine had been administered to persons aged ≥ 12 years in the United States [25] .And as of November 12, 2021, VAERS has received reports of menstrual disorders representing approximately 1 in 100,000 of the total number of P zer vaccinations.Adverse reactions to vaccination appear to be insigni cant compared to the serious life-threatening effects of infection with the virus, and there is a lack of much substantial evidence linking vaccination to adverse reactions [26,27] .
Eric Wan and colleagues in The Lancet Infectious Diseases had suggested that the overall increased risk of Bell's palsy after COVID-19 vaccination.However, to this date there is no clear evidence of a link between the COVID-19 vaccine and Bell's palsy [28] .Based on various studies of real-world data [29,30] , all approved or licensed COVID-19 vaccines provide substantial protection, although the degree of protection varies among vaccines.
However, there are several limitations to our study.First, the main limitation of our study is that it is unclear whether these adverse reactions were caused by disease or exposure to the vaccine, and there is a lack of data related to speci c medical history and menstrual histories.Second, based on the spontaneous reporting nature of VAERS, our results are susceptible to various biases, such as data omission, overreporting, and underreporting.Third, co-vaccination may suppress or enhance the immune response, and this study only refers to the report of vaccination alone and does not include the data of co-vaccination.All of the above may cause bias in our results.

Conclusion
From the signal detection results, there was a statistically signi cant association between COVID-19 vaccine and reports of adverse reactions to menstrual disorders, and COVID-19 may contribute to menstrual disorders in young adult female (30-49 years).However, our study data are from VAERS and the results may be in uenced by the number and quality of reports, so it is challenging to study menstrual disorders directly de ned as COVID-19 vaccine adverse events and should continue to track adverse reactions to vaccine in female in this age group.

Declarations
Ethics approval and consent to participate All methods were carried out in accordance with relevant guidelines and regulations.

Figure 1 Flow
Figure 1

Table 1
describes the basic characteristics of the 14431 reported cases of menstrual disorders.Reports of menstrual disorders are not mutually exclusive of each other, and multiple conditions may be involved in one adverse reaction report.The most prevalent event in both groups was Menstruation irregular, with 4626 cases (35.26%) reported in the COVID-19 vaccine group and 372 cases (28.33%) in the non-COVID-19 vaccine group.The COVID-19 vaccine group reported 2698 cases (20.57%) of Menstruation delayed,2088 cases (15.92%) of Intermenstrual bleeding, and Menorrhagia was reported only 28 cases (0.21%).The non-COVID-19 vaccine group reported 251 cases of Metrorrhagia (19.12%), 301 cases of Amenorrhoea (22.90%) and only 6 cases of Intermenstrual bleeding (0.46%).Multiple MedRDA terms can exist in one adverse reaction report, so the sum of the individual events of menstrual disorders events may be greater than the total number of reports.Whereas in the COVID-19 vaccine group, a higher proportion (42.55%) was reported in the prime age group(30-49 years).After Fisher's exact test, there was a difference between the two age groups (P value < 0.001).The interval from vaccine exposure to reported onset was reported in 11,681 cases (80.94%), with a median of 3.0 days.There were 10,877 cases (82.92%) in the COVID-19 vaccine group with an adverse reaction reporting interval < 100 days.The mean reporting interval for the non-COVID-19 vaccine group was 8 days.After Fisher's exact test, there was a difference in the reporting interval between the two groups (P value < 0.001).There are 20 non-COVID-19 vaccines associated with reported menstrual Multiple MedRDA terms can exist in one adverse reaction report, so the sum of the individual events of menstrual disorders events may be greater than the total number of reports.Fisher's exact test: α = 0.05, *P-value < 0.001, **P-value < 0.001The median age at the time of reporting was 35 years in both groups, with a mean age of 36 years in the COVID-19 vaccine group, which was greater than 16 years in the non-COVID-19 vaccine group.A high proportion of the reported age was unknown in both groups.Nearly half (48.82%) of the reported menstrual irregularities in the non-COVID-19 vaccine group were reported in the younger age group (< 20 years).

Table 2
describes the characteristics of the 13,118 menstrual disorders reported as a result of exposure to the COVID-19 vaccine.9613 cases (73.28%) were reported in relation to P zer-Biontech, 2748 cases (20.95%) for Moderna and 742 cases (5.66%) for Janssen.The reported rates of other menstrual events differed between groups (p < 0.001), except Intermenstrual bleeding, Hypomenorrhoea, Menorrhagia.

Table 3
Distribution of adverse events strati ed by menstrual disorders events and vaccination status