Cross-clade protection against HPAI H5N1 influenza virus challenge in BALB/c mice intranasally administered adjuvant-combined influenza vaccine

The avian H5N1 influenza virus has the potential to cause a new pandemic. The increasing number of recent outbreaks of highly pathogenic avian influenza H5N1 in birds and humans emphasizes the urgent need to develop a potent H5N1 vaccine. Here, we studied the immunogenicity and protective effect of a vaccine prepared from H5N1 inactivated whole virus. This vaccine was intranasally co-administered in mice with phosphate buffered saline, recombinant cholera toxin B subunit (rCTB), cholera toxin (CT), rCTB containing a trace amount of holotoxin (rCTB/CT), polyinosinic:polycytidylic acid double-stranded RNA (polyI:C), or MF59 as an adjuvant. Intranasal administration of H5N1 inactivated whole virus vaccine with rCTB, CT, rCTB/CT, polyI:C, and MF59 elicited an immunological response with both secretory IgA (sIgA) in nasal, lung, and vaginal lavage, and IgG antibody in serum, showing protective immunity against lethal H5N1 infection. Cross-clade protection was also observed in animals immunized with a vaccine derived from Anhui/01/2005(H5N1) with rCTB, CT, rCTB/CT, polyI:C, or MF59 as adjuvants that were subsequently challenged with the A/OT/SZ/097/03 influenza strain.