With the fall in H1N1 “swine flu” influenza cases recently, it has become fashionable for the media to run “What was all the fuss about” stories on the same page as “OMG, it’s going to be bad” stories. The problem with influenza is that it is one of the most unpredictable of all viruses, and while an upsurge in the number of cases can be expected as the winter flu season gets going in the northern hemisphere, the real concern is that this new pandemic virus might “turn nasty” in the second wave, just as in 1918 a much more pathogenic variant of that virus followed the relatively benign first wave of cases.
There are two ways in which this could happen. The first is that the present virus acquires spontaneous mutations which make it more pathogenic. The other possibility is that the virus recombines with a highly pathogenic influenza virus though the process known as reassortment – swapping of genes when two different strains infect the same cell. And there’s a good candidate for that out there – the highly pathogenic H5N1 avian influenza virus. Unlike H1N1, H5N1 has a hard time infecting humans, so it’s unlikely that these viruses would meet. But if they did…
The good news comes from Egypt, where H5N1 is relatively common, and a (worrying) case of H5N1/H1N1 co-infection was recently reported. The Ministry of Health has now discounted the rumour of a co-infection with the two viruses. In addition, a University of Maryland/NIH study suggests that co-infections of H1N1 with seasonal flu viruses do not produce chimeric or reassortant viruses. The H1N1 strain seems to outcompete seasonal viruses, possibly demonstrating this pandemic strain is not under biological pressure and is perhaps more efficiently communicable. Certainly, the past pattern seems to suggest that H1N1 pandemic seem to suppress outbreaks of other strains for some time.
A phase I clinical trial conducted by scientists from the University of Leicester tested 100 healthy volunteers with an H1N1 vaccine to see how their immune system responded. Trial leader Dr Iain Stephenson found 80 per cent of the volunteers showed a “strong, potentially protective” response after one dose, with more than 90 per cent showing the same response after two doses. The results suggest that one vaccine dose may be sufficient to protect against A(H1N1) swine flu, rather than two. Larger trials are now under way around the world involving up to more than 6,000 adults and children.
Reasons to be cheeful.
- H5N1 and 1918 pandemic influenza virus infection and the lungs
- Spotting pandemic influenza viruses
- How influenza pandemics get started
- The Pathogenicity of Pandemic Influenza Viruses
- The Great Flu – a free online game