A company called SEEK is pioneering a "universal flu vaccine" that would only need to be injected once and would provide T-cell immunity to all influenza strains for many years. As you probably know, current flu vaccines are annual because the influenza surface epitopes mutate too quickly for last year's vaccine to be very effective. Scientists find the current viruses circulating, predict what the major flu strains will be in any given year, and combine a few of them into a shot/spray to administer during flu season.
SEEK used computer models to compare known influenza epitopes and find ones that are conserved throughout the years. They specifically looked at ones that T-cells recognize, i.e. that have been processed internally in infected cells and presented through HLA molecules. These conserved epitopes are then mass-synthesized (rather than grown in eggs as normal flu vaccine). The trial is currently in Phase II, and shows promising results in being able to lower viral levels. It's also probably a lot cheaper and able to be mass produced.
SEEK's website...video is fairly interesting
Virophiles, which genes are likely used for this vaccine and how does induction of T cell immunity help reduce viral titers?
Since the vaccine relies on processed antigens found in the interior of cells, SEEK's conserved epitopes probably rely on chunks of viral polymerase, IFN-suppressing enzymes, or perhaps even capsid proteins (which aren't generally available on the surface of Orthomyxo). These genes are unlikely to change in sequence much over the years.
The vaccine, unlike many conventional ones, does not rely on recognition of surface epitopes and won't generate a humoral (antibody) response. Instead, it produces cytotoxic T cells which recognize and kill virus-infected cells. Memory cells of this population could recognize a subsequent infection and kill infected cells, stopping the virus from replicating. Although this response itself is not complete without the neutralizing effects of antibody-mediated immunity, activation of these cells probably hinders the initial growth of the viral population to significantly dampen the progression of the flu. It is also possible that the vaccine's ability to activate helper T cells plays a role, as these cells can strengthen the overall immune response and help activate B cells.