The trials will help doctors prepare for a pandemic
The world is still at risk from a new pandemic strain of flu according to leading scientists.
The H5N1 strain of the bird flu virus has been out of the headlines for some time but experts say it still poses a potential threat.
I have been taking part in a vaccine trial against the virus and have just received my latest jab.
It is two years since I volunteered for a clinical trial in Oxford for a vaccine against H5N1.
In 2006 bird flu was a major news story in the UK following the discovery of a dead swan with H5N1 in Scotland.
In January that year there had been the first human deaths in Turkey and the threat to Western Europe seemed palpable.
Since then, although there have been further outbreaks among poultry in the UK, there have been no human fatalities in Western Europe.
The level of media interest in bird flu has subsided - but has the threat disappeared? Not really.
Still killing people
It is very hard for humans to be infected by H5N1 - it requires very close contact with the virus.
We as a farming community, and the government, will continue to take the disease very seriously
Robert Newbery National Farmers' Union
The virus is endemic in poultry and bird stocks in south-east Asia - and 241 people have died after being infected, 24 so far this year.
However, bird flu, as the name suggests, still poses its biggest threat to poultry.
Earlier this month there was an outbreak of H7N7 bird flu at a farm 30 miles north of Oxford, forcing the slaughter of 25,000 chickens.
Robert Newbery, poultry adviser at the National Farmers' Union, said avian flu was still a serious economic and animal welfare concern - but the level of risk was quite different compared to that in countries like Indonesia and Vietnam.
"The systems in which poultry are kept in south-east Asia are completely unrecognisable compared to the UK," he said.
We did not overreact to the threat from bird flu, and we should still be worried
Professor Nick White Mahidol University
But he went on: "Having said that, while the theoretical risk to human health exists, we as a farming community and the government will continue to take the disease very seriously."
The threat may be theoretical at present - but all of the infectious disease experts I have spoken to over recent years agree that it is not a matter of if but of when the next flu pandemic will occur.
H5N1 might not eventually be the virus responsible but the pandemic will almost certainly start in animals and then mutate into an infectious human disease.
We simply don't know when that will happen - which makes it hard for the media to maintain interest.
Millions at risk
Nick White is a leading expert on infectious disease and professor of tropical medicine at Mahidol University in Bangkok and Oxford University.
He spends most of the year in Thailand where there have been 17 deaths from H5N1 but was in Oxford the day I had my third jab.
"We did not overreact to the threat from bird flu and we should still be worried," he said.
"It is fortunate that nothing has happened so far but a flu pandemic could be cataclysmic for the human race.
"If it became as infectious as Spanish flu in 1918-9 it could kill hundreds of millions of people."
Dr Alan Hay, director of the World Health Organisation Collaborating Centre at the National Centre for Medical Research in the UK, says no-one is writing off the threat from H5N1.
"We are in a state of stasis. There are plenty of infections in birds and there have been isolated human cases in Africa which is worrying.
"Thankfully, H5N1 does not readily infect people but when it does it can have disastrous consequences."
Currently, for every 10 people who get infected, six will die.
I have no regrets about volunteering for the vaccine trial.
Just because bird flu is not on the front pages any more doesn't mean that the potential threat has gone.
BBC correspondent takes part in a vaccine trial
As for the injection itself, some people expressed surprise that I volunteered for the trial and concern for my well-being.
In fact the technology used to create the prototype vaccine is very well-established and any threat to my health was vanishingly small.
I have had no ill-effects from any of the three doses I received.
The first two contained a vaccine against the Vietnam strain of bird flu and the most recent was against the Indonesian strain.
So if and when the next pandemic happens, will I and the other trial volunteers be better off than everyone else? That is a difficult question to answer.
It is possible that H5N1 pre-pandemic vaccines may offer some protection but no one can be sure until it happens.
The real point of the trial is to help scientists understand the best way of creating a vaccine when a pandemic occurs.
Only when scientists know the exact pandemic strain will they be able to tailor-make a vaccine against it and know what the right dose should be.
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