It seems illogical, but by morphing into a less virulent strain, H5N1 is more likely to cause the global pandemic experts say is overdue:
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 case fatality rate for H5N1 is now around 35%, a big improvement over the 100% of a year ago. However, the Spanish flu of 1918 killed fewer than 5% of its victims–and between 40 and 100 million people died worldwide.