The HA protein has a head and a stalk. The current flu vaccine induces our immune system to make antibodies against the head. However, the head is more prone to antigenic drift than the stalk. The stalk is conserved among many HA types; antibodies against the stalk can, therefore, protect against multiple influenza strains.
Chimeric recombinant HA: Chimeric means containing a mixture of genetically different tissues. In this strategy, a person would be vaccinated using a chimeric HA(cHA) with the stalk of the HA of a widely circulating influenza A virus and the head of the HA of a non-human influenza A virus. The non-human influenza A virus would be one that is considered to have pandemic-causing potential and we would have no immunity against it. In theory, such a vaccine would protect individuals from multiple human influenza A strains and against pandemic influenza if the HA heads of the non-human virus used for the vaccine are the same as the pandemic virus.
GlaxoSmithKline, in collaboration with Icahn School of Medicine at Mount Sinai, New York, and Duke University, North Carolina, are carrying out Phase I trials.
Recombinant stalk-specific HA: This vaccine strategy also focuses on the stalk of the HA protein. To direct the immune response to the HA stalk and not the head, the vaccine uses a modified HA that has a stalk but no head.
M2 and other influenza vaccine strategies: The M2 protein is a conserved protein, essential for viral reproduction. Inducing an immune response against this protein can stop viral replication. Such an immune response would be effective against multiple strains, making it a prime candidate for an influenza A vaccine. An M2-based vaccine—VAX102—is in Phase 1 and Phase 2 trials.
Other strategies: Bioinformatics allow us to look for conserved sequences using genetic data and computer software. Multimeric-001 (M-001) by BiondVax is a vaccine that contains nine conserved peptides (short segments of viral genetic code) from both influenza A and B viruses. This vaccine is in Phase 3 trials. Similarly, Immune Targeting Systems’s influenza A vaccine, FP-01.1, contains six conserved peptides and is in Phase 1 trials.