Beneath the totally puzzling headline "Will Pandemic Hit U.S.? Does It Even Matter?", I was struck last weekend by another "mixed message" from someone who is an authority in his field. In a guest editorial in Sunday's Richmond Times-Dispatch, the president-elect of the International Society for Infectious Diseases, Dr. Richard Wenzel, gave some background on the 1918 pandemic and the current H5N1 virus, then stated:
Is a deadly pandemic of avian H5N1 influenza inevitable? The answer is no. I would place the odds at less than 50 percent. The likely viral strategies needed to create a person-to-person spreading virus include one or more of the following: an H surface protein mutation allowing it to adapt better to human airway cells; one or more mutations in the genes controlling viral reproduction rates; a co-infection with a human strain followed by viral sex (reassortment) allowing enhanced transmission in people. While all are possible, none has occurred since H5N1 emerged nine years ago.
Those two highlighted sentences seem to oppose each other.
The last sentence leaves me with this impression: it's encouraging that these possible developments have had nine years to occur but haven't; the longer we go without an H5N1 pandemic, maybe the less chance that we'll ever get one. (Does it leave you with that impression or am I just reading it wrong?)
Yet in the same paragraph, Dr. Wenzel estimates the odds of an H5N1 flu pandemic are "less than 50 percent." My impression: Given odds perhaps approaching 50-50, I have a lot to be worried about. This conflicts with my other impression. I'm confused.
So what does he mean? Maybe he means, "While flu viruses are highly unstable and readily change genetically, H5N1 has gone nine years without changing into a human transmittable form. That's encouraging. But I suspect there's something like a 1-in-3 chance it will cause a pandemic at some point."
Maybe that's what he means. I wish he was clearer.
By the way, you may ask why I think Dr. Wenzel is inferring the odds are approaching 50-50? Because if he thought the odds are less than 5 percent (for example), he would have said, "I would place the odds at less than 5 percent."
When giving what can only be an educated guess, people usually offer an estimated range that probably captures the ultimate answer without exaggerating high or low. They usually don't overstate their estimate by an order of magnitude just to be on the safe side. When someone says "less than 50 percent," I don't think, "Oh, that means somewhere in the single digits." I think, "Oh, maybe 30-40 percent."
An added biographical note: Dr. Wenzel is also chairman of Virginia Commonwealth University's Department of Internal Medicine and is Editor-at-large of The New England Journal of Medicine. Hefty credentials all around.