According to Sir David King, telling the world that a global flu pandemic is inevitable is totally misleading. Sir David said the likelihood of the H5N1 virus mutating into a human-transmissible virus is very low.
“We have got a virus in the bird population that has gone on since 1996, and in Asia particularly there has been a lot of contact between human beings and the birds that have got that virus. Despite this, the human virus has not developed.”
Sir David added that he was fairly optimistic that bird flu was not present in wild birds (in UK). According to him, one swan in Scotland does not necessarily mean the virus has come to stay. He stressed that H5N1 is not present at all among farmed birds in the UK (poultry farms).
A recent study explained why humans cannot become easily infected with the H5N1 virus.
For the virus to make a person sick it has to reach deep down in the lungs – a very difficult task (for the virus). Most human flu viruses infect the upper-respiratory tract. H5N1 infects deep down in the lower-respiratory tract. For people to become sick, they need to surround themselves with a huge number of bird flu viruses so that some of them manage to make their way down into the lower-respiratory tract. For that to happen, you have to spend a long time in the presence of sick birds, handling them.
If a H5N1 infected person coughs or sneezes, hardly any of the viruses are expelled (because they are so deep down). That is why it is virtually impossible for one human to make another one ill with bird flu.
For the virus to spread easily among humans, it needs to change (mutate) so that it infects the upper-respiratory tract (nearer the throat). However, if it does this, because it would located further up, it would be much easier to treat.