H1N1 has yet to finish its run.

• Position: Swine Flu

If the behavior of the seasonal form of H1N1 influenza virus is any indication, scientists say that chances are good that most strains of the pandemic H1N1 flu virus will become resistant to Tamiflu, the main drug stockpiled for use against it. Researchers funded by the U.S. Army Research Laboratory and Office, Adelphi, Md., have traced the evolutionary history of the seasonal H1N1 influenza virus, which first infected humans during the 1918 pandemic. It is one of three seasonal influenza A viruses--the others are H1N2 and H3N2--at commonly infect humans. The report appears in the Journal of Health Geographics.

Within H1N1, two strains of virus circulate in humans: a seasonal form and pandemic form of influenza known as swine flu, which has sickened millions and killed thousands of people since it first emerged in North America in the spring of 2009. Over time, the H1N1 strain has developed mutations that are resistant to oseltamivir-based agents. Tamiflu is the brand name for oseltamivir phosphate. "Something happened in 2008, when drug resistance took hold," notes Daniel Janies, primary author of the study. "The drug-resistant isolates became the ones that survived all over the world. This is just static now. The seasonal H1N1 influenza virus is fixed at resistant."

He adds, "It's a pretty good bet that whatever pressure is in the...