Matt Ridley on how flu epidemics evolve away from being very deadly

It seems that another pandemic panic may be about to strike. (Thank you Instapundit, who seems a bit panic-stricken himself.)

It so happens that I have recently acquired and have been reading Matt Ridley’s excellent book, The Rational Optimist , which Johnathan Pearce has often blogged about here, in this posting, for example. (Here is a piece by Ridley, defending his book against Monbiot.)

And it further so happens that The Rational Optimist contains a very interesting passage (pp. 308-310), which I already had in mind to flag up here, even before this latest news of another flu outbreak, about the spread of infectious diseases, which explains why any pandemic panic that now materialises is likely once again to be greatly exaggerated:

In the 2000s influenza, too, proved to be a paper tiger. H5N1 strains of the virus (‘bird flu’) jumped into human beings via free-range ducks on Chinese farms and, in 2005, the United Nations predicted five million to 150 million deaths from bird flu. Yet, contrary to what you have read, when H5N1 did infect human beings it proved neither especially virulent nor especially contagious. It has so far killed fewer than 300 people worldwide. As one commentator concluded: ‘Hysteria over an avian flu pandemic has been very good for the Chicken Little media, authors, ambitious health officials, drug companies … But even as many of the panic-mongers have begun to lie low, the vestiges of hysteria remain – as do the misallocations of billions of dollars from more serious health problems. Too bad no one ever holds the doomsayers accountable for the damage they’ve done.’

I suspect this is too strong, and that flu may yet mount a serious epidemic in some form. But the H1N1 swine flu epidemic of 2009 that began in Mexico also followed the usual path of new flu strains, towards low virulence – about one death for every 1,000-10,000 infected people. This is no surprise. As the evolutionary biologist Paul Ewald has long argued, viruses undergo natural selection as well as mutation once established in a new species of host and casually transmitted viruses like flu replicate more successfully if they cause mild disease, so that the host keeps moving about and meeting new people. A victim lying in a darkened room alone is not as much use to the virus as somebody who feels just well enough to struggle into work coughing. The modern way of life, with lots of travel but also rather more personal space, tends to encourage mild, casual-contact viruses that need their victims to be healthy enough to meet fresh targets fleetingly. It is no accident that modern people suffer from more than 200 kinds of cold, the supreme viral exploiters of the modern world.

If this is so, why then did H1N1 flu kill perhaps fifty million people in 1918? Ewald and others think the explanation lies in the trenches of the First World War. So many wounded soldiers, in such crowded conditions, provided a habitat ideally suited to more virulent behaviour by the virus: people could pass on the virus while dying. Today you are far more likely to get the flu from a person who is well enough to go to work than one who is ill enough to stay at home.

Of course the pessimists could be right, in this or that particular instance. And of course we here are very pessimistic about the future course of the world’s current financial crisis. That is surely going to get far worse before it gets much better. I recall reporting here on a debate on that subject, where the other side was taking it for granted that the crisis that had just happened was now over and done with, and the only question concerned how best to “manage the recovery”. We here regard the people who talked like that, then, as the Chicken Little tendency.

And Matt Ridley himself is careful to include doubts about future flu outbreaks maybe not all being so un-apocalypctic. “Flu may yet mount a serious epidemic in some form.”

Nevertheless, interesting. And it will be interesting to see how this latest flu flare-up plays out.

via Samizdata http://www.samizdata.net/2013/04/18111/