R software program version 3

The data were analyzed using the R software program, version 3.5.2 [R Foundation for Statistical Computing, Vienna, Austria (https://www.R-project.org/)]. When comparing the patients' background characteristic, Fisher's exact test was used for nominal variables, and an analysis of variance was used for continuous variables. If the answer to a questionnaire survey item was unknown, the datum corresponding to it was excluded from statistical tests. The two-sided significance level was 5%. Demographic characteristics are presented as the mean±standard deviation or the number of cases (%).

The R software program, version 3.5.2 [R Foundation for Statistical Computing, Vienna, Austria (https://www.R-project.org/)], was used for data analyses. To compare the participant characteristics, Fisher's exact test and Student's t-test were used for nominal and continuous variables, respectively. Data from participants who provided unreadable or incomplete questionnaires were excluded from the analysis (only applicable items). The level of significance was 5% for 2-sided tests, and continuous and nominal variables were presented as the mean±standard deviation and number (%), respectively. Wald's chi-squared test was used for the multivariate analysis among factorial analyses of the long-term antibody response.