Generation of monoclonal antibodies against universally conserved fusion peptide has attracted interest in the recent past, as such antibodies are known to inhibit the HA fusion activity and to reduce virus replication in vitro and also in vivo [28, 30, 54, 62, 63] . Additionally, passive immunotherapy with Abs reactive with all strains of influenza A could be an alternative for some populations at high risk of infection, like infants, the elderly and the immunocompromised patients, who may not benefit from active vaccination. Several groups described the potential of human monoclonal antibodies against HA2 subunit and its fusion peptide with broadspectrum protection as a universal passive immunotherapeutic agent against seasonal and pandemic influenza viruses [66] [67] [68] [69] . Sui et al. [70] obtained a panel of highaffinity human antibodies that bind to the highly conserved pocket in the stem region of hemagglutinin, comprising part of the fusion peptide and several residues of the HA1 subunit. These antibodies showed a broad degree of cross-reactivity. Moreover, it was suggested that the conformational epitope on HA recognized by one of these neutralizing antibodies (F10) is recalcitrant to the generation of escape mutants [70] .