Favipiravir is approved for manufacture and sale in Japan as an influenza antiviral. It selectively inhibits the RNA polymerase of the influenza virus, an enzyme required for viral replication once human host cells are infected. COVID-19 also uses this enzyme to replicate and is classified into the same type of single-stranded RNA virus as influenza; hence, it is believed that Favipiravir may be effective in treating COVID-19.