Favipiravir shows better efficacy in treating influenza infections than oseltamivir (Tamiflu) (Takahashi, et al., 2003; Tanaka, et al., 2017) , and its efficacy in treating pathogenic avian influenza A(H5N1) and oseltamivir-resistant viruses has been confirmed in animals (Kiso, et al., 2010; Sidwell, et al., 2007) .