The 2009 influenza pandemic: promising lessons for antiviral therapy for future outbreaks.

The influenza A virus is the main circulating influenza virus in the human population. It can cause disease also in birds and other mammals and is responsible for annual epidemics and occasional pandemics. The most known and deadly pandemic was the "Spanish flu" (influenza type A/H1N1), which struck the human population between 1918 and 1919, with probably the heaviest toll ever recorded in terms of human lives. The most recent flu pandemic, caused in 2009 by the swine-origin reassortant virus (pH1N1), has raised several critical issues in terms of our preparedness in responding fast to new pandemic influenza strains. Probably, the most instructive lesson that has been learned from the 2009 pandemic, was that the speed of manufacturing and distributing an effective vaccine will not be able to keep up with the pace of a rapidly spreading pandemic virus, failing to grant accessibility to the vaccine for a significant percentage of the susceptible population, before the onset of the pandemic peak. Thus, our first and most effective line of defense against a pandemic influenza virus, particularly in the early phases, are the antiviral drugs. Here we analyze our current understanding of the influenza pandemic viruses, in general, and of the pH1N1 in particular, along with the most recent approaches being pursued to design new anti-influenza drugs.