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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Ash, flu and mad cows

Caution should be applied to predictions as well as to risks

Tim Black has an excellent article in Spiked about the hypercautious European reaction to the Icelandic volcano in April:

We have since discovered that the maximum density of ash (100 micrograms of ash per cubic metre) over the UK during the ban was one fortieth of that now deemed a safe threshold (4,000 micrograms of ash per cubic metre). In other words, the ban was nowhere near justified by what is now the official threshold.

He goes on to give some remarkable numbers from the similar over-reaction to avian flu:

Take the response to the avian flu outbreak in 2005. Dr David Nabarro, the UN systems coordinator for human and avian influenza, declared : 'I'm not, at the moment, at liberty to give you a prediction on [potential mortality] numbers.' He then gave a prediction on potential mortality numbers: 'Let's say, the range of deaths could be anything from five million to 150million.' Nabarro should have kept his estimating prowess enslaved: the number of cases of avian flu stands at a mere 498, of which just 294 have proved fatal.

And swine flu:

On 11 June 2009, just over a month after the initial outbreak in Mexico, the World Health Organisation finally announced that swine flu was now worthy of its highest alert status of level six, a global pandemic. Despite claims that there was no need to panic, that's exactly what national health authorities did. In the UK, while the Department of Health was closing schools, politicians were falling over themselves to imagine the worst possible outcomes: second more deadly waves of flu, virus mutation - nothing was too far-fetched for it not to become a public announcement. This was going to be like the great Spanish Flu pandemic of 1918-20. But worse.

However, just as day follows nightmares, the dawning reality proved to be rather more mundane. By March 2010, nearly a full year after the H1N1 virus first began frightening the British government, the death toll stood not in the hundreds of thousands, but at 457. To put that into perspective, the average mortality rate for your common-or-garden flu is 600 deaths per year in a non-epidemic year and between 12,000 and 13,800 deaths per year in an epidemic year. In other words, far from heralding the imagined super virus, swine flu was more mild than the strains of flu we've lived with, and survived, for centuries. Reflecting on the hysteria which characterised the WHO's response to Mexico, German politician Dr Wolfgang Wodarg told the WHO last week: 'What we experienced in Mexico City was very mild flu which did not kill more than usual - which killed even less than usual.'

In the same vein, I am wont to remind people of how `hundreds of thousands' of Britons were going to die of new variant CJD, the human form of mad cow disease. In fact the number of deaths never exceeeded 28 a year, has now fallen to 3 last year, one the year before, and the total is just 168. By all means let us be cautious, but can we not also treat extreme predictions about disease (or climate or pollution or anything else) with a little caution too?