Statistical analysis
Quantitative variables were described as mean and standard deviation (SD) or medians and inter-quartile ranges (IQR). Categorical variables were presented as frequencies and percentages. McNemar’s test was employed to compare the frequency of VB before and after vaccination among the same individuals. The association between selected variables and the occurrence of VB was investigated with logistic regression models, odds ratio (ORs) and 95% confidence interval (CIs) were calculated. Analyses were performed with Stata 17 (STATA Corp., College Station, TX).