Cross clade prophylactic and therapeutic efficacy of polyvalent equine immunoglobulin F(ab′)2 against highly pathogenic avian influenza H5N1 in mice

► We prepared equine polyvalent F(ab′)2 against HPAI H5N1. ► Its prophylactic and therapeutic efficacy was evaluated in vitro and in vivo. ► Its ND50 against A/Ostrich/SZ/097/04 was 2560 in cultured MDCK cells. ► 10 μg could completely protect mice infected with 100 LD50 of A/Ostrich/SZ/097/04. ► 200 μg was required to make lethally infected mice complete recovery.