CD38 and infection: MAIT cell frequencies increased in acute dengue, but reduced in influenza and HCV infections. No recovery in HCV even after successful treatment. In all infectious settings, MAIT cells displayed markers of activation (CD38, HLA‐DR, granzyme B), which decreased on resolution of infection. During dengue virus infection, CD38 expression increased over the course of infection, peaking at the day of defervescence; CD38 expression was higher on patients with more severe disease. Role for IFN‐α and IL‐15 in activating MAIT cells.