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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 Panglossian 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.

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

  • That article in Foreign Policy that you link to is by Laurie Garrett, who has turned a bit of scaremongering research on infections diseases into a lucrative career of writing books and articles, winning a Pulitzer Prize, lecturing earnest and bright eyed (but otherwise not very bright, or at least not very numerate or scientifically literate) bureaucrats, politicians, and think tank types, working as a paid advisor on a certain kind of Hollywood disaster movies, and generally as prophet of doom in chief to the American establishment with respect to infectious diseases. She is highly effective, though, at arguing to public health officials that doom is imminent unless vastly greater resources are devoted to public heath bureaucracies, above else. (I was absolutely scathing about her on this blog in 2005). The fact that she has been preaching doom for almost as long as Paul Erlich has does lead to a certain amount of scepticism.

    Hopefully on diseases instead of politics, though, a few thoughts.

    Yes, infectious diseases that are exceedingly virulent (ie kill lots of people very quickly) do tend to evolve into strains that kill fewer people and/or kill people more slowly, as that way the pathogen gets a greater chance to spread before the host dies and the pathogen dies with it. The combination of that and the buildup of resistance to the disease in the host population does mean that pandemics will likely end, and that an influenza pandemic this year will not persist into next year or the year after to the same degree. This has always been so, though, and this doesn’t prevent new strains from coming into existence through random mutation that are both highly virulent and highly contagious, and a deadly and particularly contagious strain can infect the whole world before this process really gets going.

    With respect to influenza, this happened three times in the 20th century to a sufficient extent to cause a global pandemic. The most famous one of these was in 1918, which killed perhaps 50 million people, and the other two were in 1957 and 1968, each of which killed between one and two million people. (There was also another pandemic of the same sort of magnitude in 1889). The obvious reason why 1918 was so much worse was that World War 1 had just happened, and the world was full of people who were starving, injured and otherwise in poor health, living in crowded military and refugee camps and other places of poor hygiene, and that the reason for the much higher death toll was due to the particularly vulnerable global population immediately after the first world war. It may be that the 1918 virus was in fact much more deadly and/or contagious than the 1957 and 1968 viruses, and that it would still have killed many more people without World War One. We don’t really know. it may also be that if the 1918 virus had encountered the world of 1957 or 1968, it would have had a similar impact to the viruses that actually did appear in those years. We just don’t know.

    It does seem, though that 1957 or 1968 events are much more likely than 1918 events in times of general peace. It is also the case that malnutrition is at an all time low in the world, and there is nothing, nothing, nothing, that makes you more susceptible to disease that being malnourished. The science of vaccines and the medicine of infectious diseases in general is more advanced than at any time in the past, so my sense is that influenza viruses of the 1957 or 1968 level of seriousness would kill fewer people now than then. (The fact that there have been no global influenza pandemics in 55 years since 1968 when there were 3 in the 55 years before that might indicate that we are doing something right. It also might indicate we are just lucky). Against these positive forces is the fact that there are more people in the world than ever before, and that a larger portion of these people live in close proximity to one another in cities. They live with fewer animals close by, though, and particularly fewer birds and pigs, so that part is good.

    It is entirely possible that a super duper virus much worse than the 1918 virus might come along and kill 500 million people. However, it is not likely, given that it hasn’t happened previously in recorded history, and another 1957 1968 level pandemic is much more likely. The fact that the frequency of 1957 1968 pandemics may have fallen is likely to mean that a super duper virus level pandemics is less likely too. One should be vigilant, but there are strong reasons for not panicing or panic mongering.

  • Midwesterner

    Another thought occurs to me as I read your comment, Michael. My understanding of the 1918 pandemic is that it was particularly deadly to younger, stronger people and spared many old timers. The presumed reason for this is that most of the older population had faced something similar enough in their youth that, like cowpox protected against smallpox, their immune systems were to some extent innoculated against the 1918 strain.

    So, hypothesizing, “the fact that there are more people in the world than ever before, and that a larger portion of these people live in close proximity to one another in cities” could be infecting so many people with so many less harmful variants that when a variant comes along that in the past would have been quite deadly, most people will have already faced something similar enough to help them resist it. The easy spread of flu now reduces greatly the odds of a novel strain sweeping through a population.

    Just a theory.

  • Plamus

    Midwesterner, the explanation I have encountered about the Spanish flu’s lethality on young, strong people was that it killed through cytokine storm, where the body’s immune system falls into a positive feedback loop; thus, a strong immune system gone haywire becomes a liability, managing to kill its owner along with the invading pathogens. Nowadays there are ways to deal with that. So yeah, I also believe this epidemiological “bomb” will be a dud too, but even if it were not, you’re not going to see 3-5% of the world population perish, like in 1918.

  • PersonFromPorlock

    But was the death toll in the Spanish flu epidemic centered in refugee camps and veterans’ hospitals? IIRC, it killed a lot of healthy people in ‘healthy’ environments. I could be wrong.

  • Richard Thomas

    Perhaps susceptibility to the virus is a genetic thing and those who had the susceptible gene got wiped out of the pool. If it mostly affects the young (though it seems that was only the one strain), it could take a few rounds to have full effect

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