CVI Accepts, published online ahead of print on 19 November 2008

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Clin. Vaccine Immunol. doi:10.1128/CVI.00327-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cross-reactive immunity in adult and elderly patients against clade 2 influenza A H5N1 virus strains induced by Fluval, a reverse genetic-derived adjuvanted H5N1 clade 1 prototype pandemic influenza vaccine

György Fazekas, Rita Martosne-Mendi, Istvan Jankovics, Istvan Szilvasy, and Zoltan Vajo^*

State Health Center, Budapest, Hungary (ZV, IS); Omninvest LTD, Pilisborosjeno, Hungary (GF, RMM); National Institute of Epidemiology, Budapest, Hungary (IJ)

^* To whom correspondence should be addressed. Email: zoltanvajo{at}gmail.com.

High fatality rates and multiple cases of transmission of avian H5N1 influenza viruses to humans illustrate the urgent need for an efficacious, cross-protective vaccine against H5N1 strains. Extensive genetic characterization of H5N1 strains has elucidated the natural evolutionary relationship of these strains, linking groups known as ‘clades’ to a common ancestor. Although the clades and subclades probably differ sufficiently in their antigenic structure to warrant the preparation of different vaccines, there is some evidence that cross reactive immunity can be afforded. We aimed to assess the immunogenicity of a clade 1 H5N1 (NIBRG-14) whole virus aluminum phosphate adjuvanted vaccine and determine whether it can induce cross-reactive immunity against antigenically drifted clade 2 H5N1 strains of both reverse genetics derived and wild type isolated origin. A total of 88 (44 adult and 44 elderly) subjects were studied, who received one dose (6 micrograms) of the vaccine. As judged by US and European licensing criteria based on hemagglutination inhibition, the subjects developed cross-reactive immunity against all studied H5N1 strains belonging to a different clade than the strain utilized to produce the vaccine. Our findings highlight the importance of stockpiling, since cross immune reactions induced by prepandemic vaccines will likely reduce morbidity and mortality in case of a pandemic.