The Washington Post reports:
More than a year after avian influenza emerged in East Asia, killing more than two-thirds of the people with confirmed cases, Vietnamese doctors are reporting that the mortality rate in their country has dropped substantially.
But while this is good news for survivors, it could mean the outbreak of bird flu in Southeast Asia is taking an ominous turn. If a disease quickly kills almost everyone it infects, it has little chance of spreading very far, according to international health experts. The less lethal bird flu becomes, they say, the more likely it is to develop into the global pandemic they fear, potentially killing tens of millions of people.
"The virus could be adapting to humans," said Peter Horby, an epidemiologist with the World Health Organization in Hanoi, the Vietnamese capital. "There's a number of indications it could be moving toward a more dangerous virus."
The mortality rate for bird flu in Vietnam this year is about 35 percent, almost exactly half that of last year, according to Health Ministry statistics. The mortality rate of the 1918 Spanish flu pandemic, by comparison, was less than 5 percent, but the outbreak killed an estimated 40 million people worldwide.
Officials said the drop in the bird flu mortality rate was more marked in northern Vietnam than in the south. While the virus in southern Vietnam is still killing at the same pace as last year, the rate in the area around Hanoi and elsewhere in the north has dropped from that level to as low as 20 percent. Vietnamese health experts said their suspicion that the disease is shifting is further supported by preliminary research showing a genetic change in the virus in the north resulting in the production of a protein with one less amino acid than in the south.
We must, however, beware one trick in the data. As avian flu becomes better known, more non-lethal cases will end up being reported.