Processes for increasing the viricidal activity of a fiber substrate. The fiber substrate is provided. An antiviral treatment containing a quaternary ammonium or phosphonium compound is introduced to the fiber substrate to form an antiviral substrate. The treated fiber substrate is washed and dried. The antiviral treatment may occur before or after the fiber substrate is incorporated into the HEPA filter media in a papermaking process. Also a filter made from treated fiber substrates.