Recent data support the beneficial role of T-cell response in reducing the severity of infection also in humans [85] [86] [87] [88] . Additionally, cross-reactive CTLs recognized different subtypes of influenza A virus and their protective effect was shown also in individuals, who did not have specific antibodies against a given influenza virus they were exposed to [89] . Therefore, vaccination strategies focused on generating T-cellmediated immune responses directed towards conserved epitopes of influenza virus are also considered.