I have been doing radio interviews today about the flu pandemic.  Essentially the message is that while there have been about 30,000 cases of this pandemic strain causing an infection, there have been fewer than 0.5% deaths.

Now, while this is a terrible situation for the families of the bereaved, it is only slightly above the number of deaths we might expect from one of the annual strains of flu (which, incidently should also be called pandemic strains, but there are connotations with using the word).

Digging deeper into the figures and you see a strange bias in the frwquencies of deaths in different countries. In mexico the ratio of deaths to incidences of the disease is about 2%, which is very high indeed.  If this this frequency were maintained globally , then we would have a real panic situation.  However, after more than 800 cases reported in the UK, there are still no reported deaths.  This would make the disease very benign indeed.

So, why the discrepancy?

Well, one possibility is the initial viral load. In Mexico, it might have been the case that those who died were exposed to large initial concentrations of the virus and this caused complications over-and-above what might be expected.

Another possibility is that those who died in Mexico were in poor health originally.

It might also be that they didn’t receive good medical treatment (the H.S.E. here in Ireland is giving all patients Tamiflu).

It might also be (and this is a bit of a personal theory) that the initial strains were more ‘virulent’ (disease causing) than later strains of the disease.  A virulent strain tends to burn itself out. Ebola viruses kill those that they infect and they kill them quickly.  This is too quickly for the virus to spread very far, so Ebola outbreaks tend to be epidemic and localised.  The strains that are circulating now are more benign and with the patient not feeling too bad, they are spreading more easily and more widely.  So far only about half a dozen countries have reported deaths - Mexico, USA, Canada, Colombia, Costa Rica, Chile (maybe others). This might indicate that the virus is mutating to a strain that is less virulent (this is advantageous to the virus as it assists in the spread of the virus).

Lastly (though there may be other elements), it may be that there is some host genetic element that makes them more susceptible to this strain.

Either way, wash your hands and stay safe.