Jeremy Farrar is the director of the Oxford University's Clinical Research Unit in Ho Chi Minh City, which is based at the city's main Tropical Diseases Hospital.
Working with colleagues at the hospital and the research unit, he is one of a team of scientists who first published case reports of patients who presented with H5N1, the current strain of avian influenza.
He explained to Panorama how the H5N1 virus affects people and how it may be evolving.
It starts with common, non-specific symptoms, which is very important because at that stage its impossible to tell the difference between a very nasty Avian influenza and a common cold.
Probably you have few symptoms, maybe a slight fever, maybe a cough, maybe a headache and then that seems to progress and very rapidly you can deteriorate.
The virus probably invades through the mouth or through the nose and then invades the lungs and from there spreads to the rest of the body.
One of the differences between this influenza and what we commonly regard as the flu is that the damage is much more widespread.
In the end, all of the organs of the body are infected.
In this virus so far 50 or 60 per cent of people who get the infection die, and of course that virus dies with the patient and its absolutely tragic for the patient and their family but in terms of spreading the virus to other people its actually very good news at a population level because that virus can't go on.
The worry would be if the virus started killing slightly fewer people but infected more, then we have the chance for a global pandemic."