The swine flu is spreading silently and slowly throughout the World, but it does not make headlines any more -or not yet again, at least. So far, a total of 8565 cases have been reported in five continents, and 73 people have died of it. The last death reported is a 55-years-old teacher in New York, who passed away after a five-day respiratory crisis.

This influenza is not as deadly as initially thought, if we look at the numbers: given the above numbers we obtain a death rate of less than one in a hundred -or, to be precise, 8.52+-0.99 per mille, where the uncertainty given is just statistical.

In truth, the 0.0085 rate is probably an overestimate. The number of people who contracted the virus must be much larger than the reported one, because it is quite likely that many who reacted well to its attack did not bother reporting it -or did not even realize of having been affected.

An accurate death rate is probably beyond our measurement capabilities. It is affected by a uncertainty which is usually ignored, but often large: the ill-defined nature of what is being measured. What is a death rate, after all ? How do we define "attacked by the virus" ? What is the concentration of viral units above which we count somebody as affected by it ? How long do we have to monitor affected patients before we declare they have survived ? Do deaths occurring later on because of the consequences of the disease count or not ? Where do we draw a line ?

Despite all those caveats, what we measure is still a useful number, because it can be compared to others computed with similar biases. As scientists know, systematic uncertainties have the pleasing property of canceling out, at least in part, if one takes ratios of measurements affected similarly by them.

So the swine flu appears much deadlier than the other less publicized strains occurring every year, which typically have death rates of about one in a thousand.

If H1N1 were to spread massively, we would probably see a large number of deaths especially in non-developed countries. I am not a microbiologist, but it does not take one to imagine a situation similar to the one which caused millions of deaths in 1918 -although back then, the World was just recovering after the dire straits of World War I, and the virus easily overcame weakened bodies unable to fight it well.

The death rate of the 1918 flu outbreak was a scary 2.5 percent: three times larger than the H1N1 swine flu. The new virus has a few advantages with respect to its 91-year-old relative, though: a virus nowadays may go round the World in the matter of a couple of days, and there is a much larger human contact now, because of the increased urbanization and larger population density we have now. So it might take much less for H1N1 to become a pandemic, catching us unprepared. Got Relenza or Tamiflu ?