CD4 and COVID-19: The pioneering use of mRNA vaccines in clinical practice has raised concern for a potentially increased risk for HZ reactivation because HZ reactivation occurs in the setting of a decline in cell-mediated immunity [34,35], and mRNA COVID-19 vaccines elicit the activation of CD4+ and CD8+ T-cells and a TH1-mediated immune response, which could potentially interfere with the T-cell-mediated immunity directed against VZV [36,37].