Adjuvants for pandemic influenza vaccines.

The use of adjuvants is being explored as a means of improving vaccine immunogenicity. This is particularly important for the development of vaccines against potential pandemic influenza virus strains. Adjuvants act by prolonging the exposure time of antigen to the immune system, enhancing the delivery of antigen to antigen-presenting cells, or providing immunostimulatory signals that potentiate the immune response. Aluminum salts are the only licensed adjuvant in the United States, but the combination of these salts with inactivated influenza A/H5N1 antigens has had little effect on seroresponses. Several oil-in-water adjuvants, including MF59 and AS03, have significantly enhanced immune responses in healthy adult vaccine recipients to inactivated influenza A/H5N1. Additional studies are needed in vulnerable populations (younger and elderly persons, pregnant women, and immunocompromised patients) to confirm the safety and enhanced immunogenicity of these promising formulations. A number of other adjuvants are under investigation to evaluate their ability to improve the immunogenicity of inactivated vaccines targeting influenza A/H5N1.