Statistical analysis

K-means clustering, using Gower’s distance and the Forgy algorithm [34], was used to cluster vaccine-related questionnaires for the participants (n= 1,768). According to previous findings, Gower’s distance method is adequate when ordinal variables are included in the clustering. The chi-square test and analysis of variance (F-test) were used to determine the differences in baseline measurements according to 5 vaccination-related clusters. Continuous variables are shown as mean and standard deviation, whereas binary/categorical variables are shown as frequencies and column percentages. We conducted logistic regression to assess the association between mental health status and 5 clusters related to COVID-19 vaccination, and the adjusted odds ratio (ORs) and 95% confidence intervals (CIs) were reported. The ORs were adjusted for age, sex, marital status, education level, income level, current smoking/drinking status, regular physical activity, previous chronic disease history, and baseline study year (2013-2018). All analyses were conducted in R version 3.6.3 (R Core Team, Vienna, Austria)with the “cluster” and “fpc” packages.