CD38 and viral infectious disease: Multiple reports provide evidence that unswitched memory B cells are protective during viral infection; the frequency of unswitched memory B cells negatively correlated with disease activity during SARS-CoV-2 infection (22), unswitched memory B cells in principal component analysis of clinical biomarkers clustered with patient discharge from the hospital (25) and, although identified by different phenotypic criteria (CD38-CD24+), unswitched memory B cells negatively correlate with symptom duration (29).