One of the main challenges presented by influenza is the virus’s tendency to undergo genetic change. Seasonal influenza virus strains change frequently and, as a result, new vaccines are needed each year to provide protection against the new strains. That’s problematic for two reasons, however: first, it takes time to develop new vaccines, even though the techniques and procedures for doing so are well-established; and second, even after a vaccine is developed and mass-produced, it still has to be distributed and administered to millions of people. Both of these steps require a lot of time, an efficient infrastructure, and a large, coordinated effort to achieve.
In response, researchers are trying to develop an influenza vaccine that can provide broad protection against influenza–including future strains–so that a single vaccination would be enough to protect an individual from the seasonal flu for three, five, perhaps even ten years or more.
Past influenza vaccines have targeted a particular segment of the hemagglutinin (HA) protein that allows influenza viruses to attach to and enter cells. (There are many different hemagglutinin subtypes; avian flu, for example–H5N1–is of hemagglutinin subtype 5, while the novel H1N1 “swine flu” is of type 1.) To this point, flu vaccines have focused on the “globular head” of the HA protein, the part of its structure most frequently targeted by antibodies to influenza. Unfortunately the globular head, like influenza viruses as a whole, is subject to frequent genetic changes–so researchers are focusing on a different part of the HA protein’s structure.
That segment is called the HA “stalk,” which tends to be more genetically stable than the globular head. Even when an influenza virus as a whole undergoes antigenic change, it’s likely that the HA stalk will remain relatively stable. That makes it a good target for an influenza vaccine designed to protect against multiple strains. Of course, there’s yet another challenge: the HA stalk is somewhat “hidden” from the immune system’s view by the globular head. So, in an attempt to generate broad immunity against multiple influenza strains, researchers developed an altered molecule without the HA globular head, then vaccinated mice using their “headless” construct.
When challenged with exposure to a particular strain of influenza, the mice showed improved reactivity against other strains when compared to mice vaccinated with “complete” HA protein. Although more research is needed, the study’s authors stated that headless HA vaccines may be able to provide protection against multiple influenza stains, possibly against many years’ worth of seasonal flus.
Steel, J., A. C. Lowen, T. Wang, M. Yondola, Q. Gao, et al. 2010. An influenza virus vaccine based on the conserved hemagglutinin stalk domain. mBio 1(1):e00018-10. doi:10.1128/mBio.00018-10.
Link to full article: http://mbio.asm.org/content/1/1/e00018-10.full