CD19 and common variable immunodeficiency: In our study CVID responders showed significantly higher levels of serum IgG before immunoglobulin substitution therapy, and a trend towards higher percentages of CD19+ lymphocytes and higher percentages of MZ-like IgM memory B cells as compared to CVID non-responders, indicating that together with new mRNA vaccine technology less severe impairment of immunity might be responsible for intact IgG responses to BNT162b2 vaccination in these patients.