by revere, cross-posted at Effect Measure

With the advent of flu season the perennial question of the “next pandemic” is again making an appearance, although I think it is more of a cameo appearance than a substantive one. WHO, CDC and numerous state health departments are warning citizens about seasonal flu, still a major public health problem, and the continuing threat of emergence of a novel flu virus to which the earth’s population has little or no immunity. There is something both plaintive and formulaic about these warnings. Seasonal flu is with us every flu season (hence its name) and the feared pandemic of bird flu has yet to materialize. Meanwhile there are great many “important things” claiming our attention, not the least of which is a global financial system in meltdown. People have been warning of a potential financial crisis for years, but it didn’t happen. Until now.

So what about a bird flu pandemic? It is just as hard to predict as a financial crisis. The world of public health has been trying to prepare for the possibility of a pandemic with the most likely culprit, the H5N1 subtype of influenza A. H5N1 is endemic in poultry and avian wildlife in many countries. It infects humans infrequently (one would have to say rarely, given the prevalence of exposure) but when it does it is highly virulent. Case fatality ratios are well over 50%. But so far it is not easily transmissible between people, the last step to making this a truly horrific pathogen. Most countries and most states in the US now have some kind of pandemic plan but these are mainly on paper. There is an old military adage that most battle plans don’t survive the first engagement with th enemy, and this is certain to be true with most pandemic plans as well. The geographic spread of bird flu to poultry and humans has stabilized, but that is small comfort for flu scientists. There are billions upon billions of viruses replicating out there in one kind of host or another, and each replication is an experiment in finding a recipe for efficient replication in a new host. The number of possible combinations is unimaginably large so it is not a given, even with all that natural experimentation going on, that a deadly recipe is inevitable or imminent.

Human cases of H5N1 first appeared in Hong Kong in 1997. A heroic effort on the part of Hong Kong public health and veterinary authorities involved culling nearly every poultry animal on the island and the world appeared to have dodged a bullet. But out of nowhere H5N1 reappeared in poultry in 2003 and the incidental human cases started appearing along with it. Where it was in the 6 years prior to that we don’t know. But it wasn’t gone. The relative quiet (relative to the several years preceding) shouldn’t be interpreted as a war that has been won. We have no idea what controls the dynamics of this disease.

Ninety years ago, just about this time, the 1918 pandemic’s ferocious second wave was reaching its peak. It seemed to come out of nowhere (although retrospectively it was visible the previous spring) and fell like a giant hammer. It’s a reminder that things can turn on a dime in this world. I don’t expect this will get anyone’s attention. There is too much noise out there. But it doesn’t hurt to remind everyone.

Now back to our regularly scheduled programming.