During our influenza lecture, we talked about the difficulty in designing flu vaccines due to the rapid mutation of the influenza viruses. Because the virus is constantly changing, vaccines must be continuously created to protect against potential influenza pandemics. Researchers can only give their best estimates as to which flu strains might be the most threatening when preparing each year's "flu shot".
Avian influenza is of particular concern, as it is extremely infectious and deadly. However, researchers at Saint Louis University's Center for Vaccine Development have examined a vaccination technique that may be effective in enhancing human immunity to H5N1. The researchers found that combining a first dose of stockpiled avian influenza vaccine from previous years with a second dose of a vaccine matching the current influenza strain gave a strong immune response. This method, aside from producing a strong immune response, would be useful because of the already produced first dose that would come from the 20 million doses of avian influenza vaccine that the U.S. stockpiled during the 2004 H5N1 outbreak in Vietnam.
It seems that this "priming" and "boosting" vaccine combination could be important in preventing future H5N1 epidemics. However, it is important to note that the researchers found that the strongest immune response occurred when the two doses were the longest distance apart (180 days). This would not be particularly useful in response to an epidemic, since the need to immunize would be time-sensitive. However, it could be useful in immunizing people who have not been affected by the virus, but are in high risk groups for becoming infected.