Antigenic and genetic characteristics of H5N1 viruses and candidate H5N1 vaccine viruses developed for potential use as pre-pandemic vaccines, March 2007.

The H5N1 viruses chosen for development of pre-pandemic candidate vaccine viruses are representative of antigenically and genetically distinct groups of viruses that have infected humans primarily through contact with ill or dead H5N1-infected birds. These representative candidate H5N1 vaccine viruses have been prepared by reverse genetics and safety tested prior to release for production of pilot vaccine lots that may be used for experimental studies and for stockpiling by governments in advance of a possible H5N1 pandemic, should such a national policy exist. Companies are recommended to consult individual national authorities on the H5N1 strains to be used. Decisions should be based on the epidemiology of the circulating H5N1 viruses that are described below.