Preparing for a possible pandemic: influenza A/H5N1 vaccine development.

The ongoing epizootic of highly pathogenic influenza A/H5N1 viruses has ignited global efforts to develop human vaccines against these strains. Clinical trials of subunit H5 vaccines (recombinant hemagglutinin, subvirion, and purified surface antigen preparations) suggest that the high dosages of hemagglutinin are necessary to stimulate immune responses. Exciting results obtained using adjuvants (MF59 and others) and whole virus preparations point the way toward future vaccine development efforts. Other approaches (live attenuated vaccines, cell culture grown virus, DNA constructs, and conserved epitopes) are also being explored. Whether or not a pandemic spread of the A/H5N1 virus occurs, lessons learned as a result of these activities will better prepare us for future pandemics, as well as for interpandemic influenza.