CD19 and COVID-19: However, the multivariate logistic regression analysis demonstrated that only 2 variables correlated with the NAb titers after COVID-19 vaccination, including the urea level (OR = 2.32, 95% CI = 1.08–4.98, p = 0.03) and the increment in CD19+ B cells between the second and first vaccinations (OR = 1.96, 95% CI = 1.19–3.705, p = 0.03) (Table).