A method for treating and/or preventing a proprotein convertase subtilisin/kexin type 9 preproprotein (PCSK9)-susceptible viral infection comprising increasing a PCSK9 activity and/or expression in a biological system infected by the virus, whereby the increased PCSK9 activity and/or expression treats and/or prevents the viral infection in the biological system. Methods of classifying subjects, methods of screening and kits therefore.