While Swine Flu is the biggest trending topic on Twitter this morning, and many commentators are predicting untold carnage, it’s worth noting that the symptoms and transmission of the swine flu from human to human is much like seasonal flu: commonly fever, lethargy, lack of appetite and coughing.

Some people with swine flu have also reported runny nose, sore throat, nausea, vomiting and diarrhoea. That’s according to the US Centre for Disease Control and Prevention (CDC). Of course in the very young or very frail, these symptoms can be enough to make an individual extremely ill, or even be fatal. This latest variant of the virus is also thought to have killed some otherwise healthy adults. But fatalities are still thought to be rare as a percentage of all infections.

So how come there have been up to 152 deaths in Mexico already, and none in the rest of the world? According to a WHO expert interviewed on The Today programme on Radio 4 this morning, it’s highly likely that although still a scary number, 152 is a very small percentage of the number of people actually infected with the virus in Mexico. “There could be 10,000, 15,000 infections,” he said, “making the number of deaths a relatively small percentage, though of course we should still be very concerned at any deaths, regardless of the numbers.”

He said the numbers of deaths are also skewed by the fact that only those infected persons in hospital — i.e. those who are very ill already — tend to be counted towards the number of known cases. The far larger body of cases, where people develop far less severe symptoms, is much harder to track in the early stages of the infection’s progression.

The spokesperson said that the reason there have not yet been any deaths outside of Mexico — where the infection began — is probably because not enough people have contracted the virus, so the law of averages, and the fact that the NHS is able to focus its resources on a small number of people, means that there have not yet been any fatalities outside Mexico’s borders.

That’s partly because for most adults, swine flu responds well to drugs including amantadine, rimantadine, oseltamivir and zanamivir. So as long as it is identified fairly quickly, and the right course of treatment is available, the prognosis is actually good.

So while any deaths are tragic, as President Obama said, so far there is “cause for concern but not alarm”. It remains highly unlikely that even those catching the virus would become very seriously ill.

Don’t take my word for it — read the Guardian’s excellent piece here.