PERSPECTIVES — TOWARD A FASTER VACCINE RESPONSE TO PANDEMIC INFLUENZA

Influenza is a major cause of morbidity and mortality in most areas of the world. In a typical year, up to 500,000 deaths are caused by influenza globally (∼10% occur in the US), but these numbers can be much higher during pandemics. Estimates based on historical data from previous pandemics, suggest that as many as 2 million people may succumb in the US alone (Nichol and Treanor, 2006). Therefore, pandemic influenza preparedness will be critical to limiting severity and an effective vaccine will be a cornerstone in this effort. The paper by Ye et al. in this issue has investigated a DNA vaccine approach as a possible means to rapidly respond to the current swine-origin influenza virus (S-OIV) pandemic. New influenza strains frequently emerge through point mutations that arise during virus replication. These drifted strains are closely related to those that circulated during the previous year but often antigenically altered so that vaccine composition must be changed. Markedly different flu viruses can enter human circulation via zoonotic transfer from animals or reassortment of genes to produce chimeric viruses derived from human and animal strains. These shifted strains have substantially greater antigenic difference from concurrent circulating strains and a lack of cross-reactive immunity leaves people more vulnerable to severe disease. Such was the case for the Spanish, Asian, Hong Kong and Russian pandemics of 1918, 1957, 1968 and 1977, respectively. Fortunately, though, under normal circumstances influenza is preventable through the use of an effective vaccine. The strains in seasonal flu vaccines are re-evaluated each year and frequently changed