FURIN and influenza: It was previously proven that proteolytic cleavage of the influenza virus hemagglutinin (HA) and the S of SARS-CoV or MERS-CoV by cellular serine proteases, such as furin and/or TMPRSS2, could be addressed for the treatment of influenza, SARS-CoV, and Middle East respiratory syndrome coronavirus (MERS-CoV) infections [17,18,19,20].