By Matt McGrath
Science reporter, BBC News
Avian flu experts meeting in Paris have been told that a viable vaccine against the human form of the disease could take 10 years to develop.
Close contact with infected birds can spread the virus to humans
Dr David Fedson, a retired professor of medicine, told the conference that there were well-documented problems with the H5N1 virus when it came to making a vaccine.
Scientists normally grow such a vaccine from an inert form of a virus, using chicken eggs as their favourite growing medium.
According to Dr Fedson, who also worked for a number of years in the vaccine manufacturing industry, the vaccine produced from H5N1 was proving particularly difficult to grow up.
It was also proving ineffective at stimulating an immune response that would give a person a good defence against bird flu.
He told BBC News: "Right now, worldwide, we can produce 300 million doses of seasonal flu vaccine, but it turns out that the H5N1 vaccine is so poorly immunogenic and replicates so poorly that... we could immunise globally, with six months of production, about 100 million people.
"From a public health point of view this is catastrophic," the former professor of medicine at the University of Virginia School of Medicine, US, said.
"We have had reverse genetics H5N1 viruses available to work with for three years and after three years this is all we can say: 'We could produce enough vaccine worldwide, for 100 million people'. Is that good enough? I don't think so."
Dr Fedson's views were echoed by Professor Albert Osterhaus, a leading European virologist based at the Erasmus Medical Centre, Rotterdam.
He was involved in decoding the virus behind the Sars (Severe Acute Respiratory Syndrome) epidemic.
He told the meeting that a global influenza task force was needed to get to grips with the situation.
On the subject of a vaccine, he said: "If a pandemic were to happen tomorrow, we would not have a vaccine; at least not a vaccine with which we could vaccinate the European population or the American population - and we need a vaccine for the world.
"Basically, if we don't invest now in suitable clinical trials, there will be a shortage of vaccine - if we have a vaccine at all."
Governments were in denial about the potential danger and this was the root of the problem, according to Dr Fedson.
"If you look to the UK, France, the Netherlands and Italy (countries with companies that produce vaccine) - are any of the health authorities in these counties spending public funds on clinical trials of H5N1 vaccine? The answer is 'no'.
"Not a single pound sterling is spent by the Department of Health in the UK on clinical trials - why is this so? Contrast this with spend on the Eurofighter for European defence, a weapon system no longer needed. Our priorities have got mixed up. Governments are feckless."
"Why can't governments be driving the boat on this? Especially in the UK. Your experience of developing the meningitis vaccine is a role model of how to do it. The Department of Health said they would be in control, be in charge of data; they said here's the schedule and we have the money - from A to Z, the process worked like a charm."
There was no point blaming the vaccine manufacturing companies, said Dr Fedson, who was at one time director of medical affairs at Aventis Pasteur.
"We've got to get away from the fantasy that pharmaceutical companies are charities - they make hard-nosed decisions about where they are going to make their profits.
"Some companies have sensed that by building supplies or stockpiles of pre-pandemic vaccine, they can make easy money by just selling millions of doses to governments - they don't have to hire a sales force.
"They're doing good business based on governments being fearful of what might happen if they are perceived to have done nothing.
"When governments say they have bought, say, eight million doses of pandemic vaccine, all they are doing is buying a bucket full of antigen, because we really don't know how it is going to be formulated and there is no licensed, registered pre-pandemic vaccine in the world.
"They are hedging their futures."
The First International Conference on Avian Influenza in Humans has been taking place this week at the Pasteur Institute in Paris.