RESEARCH ARTICLE Protection against H5N1 Influenza Virus Induced by Matrix-M Adjuvanted Seasonal Virosomal Vaccine in Mice Requires Both

Background It remains important to develop the next generation of influenza vaccines that can provide protection against vaccine mismatched strains and to be prepared for potential pandemic outbreaks. To achieve this, the understanding of the immunological parameters that medi-ate such broad protection is crucial. Method In the current study we assessed the contribution of humoral and cellular immune responses to heterosubtypic protection against H5N1 induced by a Matrix-M (MM) adju-vanted seasonal influenza vaccine by serum transfer and T-cell depletion studies. Results We demonstrate that the heterosubtypic protection against H5N1 induced by MM adju-vanted vaccine is partially mediated by antibodies. The serum contained both H5N1 cross-reactive hemagglutinin (HA)- and neuraminidase (NA)-specific antibodies but with limited virus neutralizing and no hemagglutination inhibiting activity. The cross-reactive antibodie