Infection with the H5N1 bird flu is both more prevalent and not as deadly for humans as had been previously thought, according to a paper that has just been published ahead of print by the research journal Science. But before you relax your guard, consider this piece of context: most flu specialists have long assumed that the H5N1 flu strain was probably not as deadly as the current WHO case mortality rate of 59% might suggest—a fact that Helen Branswell so clearly explained on February 14 in her extensive report on the subject for Scientific American.

However, as Helen reports, if in fact H5N1’s true mortality rate in a future pandemic is much lower than the current case mortality rate, perhaps as low as 5.9% or even 0.59%, the death toll could still prove devastating. The horrific 1918 pandemic killed approximately 2% of all the people it infected—many of them young men and women in the prime of their life—while the regular seasonal flu has a mortality rate of around 0.1%. So an H5N1 pandemic with a greatly attenuated morality ratio could easily be six times more deadly than a normal flu season.

The point is, no one knows for certain. “I'm sure it's less than 60 percent but it's still too high for the world to tolerate a (human-to-human) transmissible H5N1 virus," Robert Krug, a well-known influenza researcher at the University of Texas at Austin, told Helen. Unfortunately, the continuing fixation on the exact potential death toll has, in Krug’s estimation, taken away from the key message revealed in recent, as yet unpublished studies: for the first time, we have solid evidence that the H5N1 virus can adapt to spread in mammals, including perhaps humans.