The most readily available drugs against influenza have abruptly declined in effectiveness in the past decade, and flu vaccines offer elderly people only modest protection against illness, according to two new analyses.
The findings lay bare limitations of both countermeasures, sounding a discouraging note as flu season draws near in the Northern Hemisphere.
One study finds that viruses are becoming resistant to drugs known as M2 blockers or adamantines. Those drugs, which impede the flu virus from copying itself, have been used to treat and prevent infections, mainly in the elderly, for nearly 4 decades.
"We can see resistance increasing to this class of drugs," says virologist Rick A. Bright of the Centers for Disease Control and Prevention (CDC) in Atlanta. "Fortunately, we have other drugs, like Tamiflu."
But Tamiflu, the trade name for oseltamivir, and its chemical relative zanamivir (Relenza) are patented, more expensive than M2 blockers, and manufactu