Not knowing which particular genetic variant will sustain human-to-human transmission makes our ability to formulate a vaccine in advance all the more diffi cult. An inactivated vaccine that induces not only high levels of neutralizing antibody to surface proteins but also CD8 Tcell response against well-conserved antigens derived from internal viral proteins might provide superior protection in an epidemic or pandemic. In cases of established intracellular infl uenza A infection, infected cells are mainly eliminated by effector CD8+ T cells (CTLs) (18) . Any vaccine that will induce and direct these CTLs to the site of infection and generate a long-lasting memory response will be more effective for mounting protection against a pandemic form of infl uenza (H5N1). Inactivated vaccines need to be presented to the host's immune system with an appropriate adjuvant, but inactivated vaccines that use an adjuvant currently approved for human use (alum or MF-59) usually have lower immunogenicity than live attenuated vaccines (10) . Therefore, the pursuit for other nontoxic adjuvants, including TLR ligands and agonists that could effectively activate dendritic cells for the presentation of viral antigens to CD4 and CD8 T cells, should vigorously be continued. Use of cytokines such as IL-12 or IL-18 may enhance the immunogenicity of antiviral vaccines. Recombinant fowlpox vaccines coexpressing HA of subtype H5N1 and chicken IL-18 have been shown to induce complete protection in vaccinated chickens (19) . Use of adjuvants may enhance broader cross-reactive immune responses among infl uenza viruses (20) .