JAK1 inhibitory activity of ruxolitinib has been related to reduced immune surveillance and the association with higher incidences of opportunistic infections and particularly reactivation of Herpes zoster, but also reactivation of tuberculosis, cryptococcal meningoencephalitis, Pneumocystis jirovecii pneumonia, hepatitis B, toxoplasmosis, or cytomegalovirus retinitis have been reported underscoring the importance of increased vigilance [73,74,75,76,77]. This evidence concerns the gene JAK1 and hepatitis B virus infection.