Swine flu pandemic killed 15 times more than thought

The swine flu pandemic of 2009 has been derided as a "wimp" pandemic. Well, how's this for wimp: it probably killed 284,400 people ? eight times the number officially reported ? within its first 12 months of touring the world.

Because few cases are tested, we know the official numbers were an underestimate. But Fatimah Dawood of the US Centers for Disease Control and Prevention in Atlanta, Georgia, and a host of colleagues around the world sought to derive the global toll by putting together confirmed measurements of rates of infection at 17 places in 13 countries, poor and rich, together with known variations in death rates in rich and poor countries.

In fact, uncertainties in the data mean deaths might have been much higher than 284,400 ? they might have reached some 575,400. A normal seasonal flu takes 250,000 to 500,000 lives a year globally but, crucially, 87 per cent of the pandemic dead were people younger than 65. In ordinary winters, 90 per cent of flu deaths are in people aged 65 or over.

That means the years of life lost to the pandemic were a staggering 9.7 million globally ? 3.4 times as many as during a regular flu season.

Five million of those lost years were in Africa and Southeast Asia, due to higher death rates from respiratory infections. Dawood's team says this shows how much more flu vaccine and antiviral drugs are needed in those regions. Supplies for both are currently low to non-existent in both places.

"This is a good analysis" and is probably a good rough estimate of the deaths from the pandemic, says Lone Simonsen of George Washington University in Washington DC, who wrote an accompanying commentary. But the analysis is based on generalising the measured rates of infection and death from a few countries to other countries, which inevitably involves uncertainty. In particular, says Simonsen, the relative likelihood of someone dying once they are infected is hard to get right, and may have been underestimated for "middle income" countries such as Mexico.

Simonsen is involved in another study, also involving the CDC, which will look at real data for pandemic deaths in more than a dozen countries that have such measurements. The problem, says Simonsen, is that many countries do not have such measurements, and those that do can take time to collect the numbers ? even US figures became available only a few months ago.

Journal reference: The Lancet Infectious Diseases, Dawood's paper: DOI: 10.1016/S1473-3099(12)70121-4; Simonsen's commentary: DOI: 10.1016/S1473-3099(12)70152-4

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