The vaccine to prevent every strain of flu

British scientists are on the verge of producing a revolutionary flu vaccine that works against all major types of the disease.

Described as the 'holy grail' of flu vaccines, it would protect against all strains of influenza A - the virus behind both bird flu and the nastiest outbreaks of winter flu.

Just a couple of injections could give long-lasting immunity - unlike the current vaccine which has to be given every year.

The brainchild of scientists at Cambridge biotech firm Acambis, working with Belgian researchers, the vaccine will be tested on humans for the first time in the next few months.

A similar universal flu vaccine, being developed by Swiss vaccine firm Cytos Biotechnology, could also be tested on people in 2007 - and the vaccines on the market in around five years.

Importantly, the vaccines would also be quicker and easier to make than the traditional jabs, meaning vast quantities could be stockpiled against a global outbreak of bird flu.

Martin Bachmann, of Cytos, said: "You could really stockpile it. In the case of a pandemic, that would be a huge advantage.

"If you were to start making a traditional vaccine at the start of a pandemic, there is no way there would be enough."

The Government believes a bird flu pandemic is inevitable, killing 50,000 people in Britain alone.

However, it acknowledges that the bug could be much more lethal - infecting one in two people and claiming more than 700,000 lives.

Normal winter flu can also kill, claiming up to 12,000 lives a year in the UK.

Although a vaccine exists, constant changes in the virus's appearance have until now made it impossible to create just one flu vaccine.

Instead a new vaccine is put together each year to protect against the particular strains circulating at that time.

In addition, the virus used in the jab is grown in hen's eggs - a time-consuming process that yields just one shot of vaccine per egg.

The new jabs would be grown in huge vats of bacterial 'soup', with just two pints of liquid providing 10,000 doses of vaccine.

Current flu vaccines focus on two proteins on the surface of the virus. However, these constantly mutate in a bid to fool the immune system, making it impossible for vaccine manufacturers to keep up with the creation of each new strain.

The universal vaccines focus on a different protein called M2, which has barely changed during the last 100 years.

The protein is found in all types of Influenza A, including the current bird flu and the virus that caused the 1918 Spanish flu pandemic which killed up to 50 million across the globe.

Normally, such vaccines would have to go through at least five years of human tests before going on the market. However, if a bird flu pandemic occurs before that, they could be made more quickly available.

Zurich-based Cytos, which is also developing anti-smoking and obesity vaccines, has showed that its version of the jab stops mice dying from a dose of flu strong enough to kill them four-times over.

The vaccinated animals were also spared the fever that normally goes along with flu.

Although it is too early to say what the effect would be in humans, an initial course of two or three shots could provide long-lasting immunity, topped up with booster shots given every five to ten years.

Dr Ashley Birkett, of Acambis, said: "It wouldn't be that one shot protects for life but you would need fewer doses over your lifetime."

In addition, the jabs could be produced in vast quantities and stockpiled ahead of a flu pandemic - or even given to people in advance.

In contrast, a traditionally-produced vaccine, matched to the specific strain of flu, would not be available until around six months after the start of the pandemic.

The new vaccines only protect against influenza A - the version of the bug responsible for pandemic flu and the most severe cases of winter flu.

However, it may also be possible to create a similar jab against influenza B, which causes a milder form of winter flu.

Professor John Oxford, Britain's leading flu expert, said the development of a universal vaccine was the "holy grail" of flu research.

He added: "If you get a M2 vaccine which protects against the whole caboodle in the same vaccine, the possibilities are huge."

But, others cautioned that there is no guarantee that the jabs would be as effective in humans as it has been in animals.

Virologist Professor Ian Jones, of the University of Reading, said: "It is an encouraging technique which may have a role to play but it is too soon to assume that it will translate into a universal vaccine in the human population."

Dr Jim Robertson, a vaccine expert from the government-funded National Institute for Biological Standards and Control, said the main advantage of a universal jab would be lasting immunity.

"If it works, it will be lovely," he said. "The best result would be that it would last for a long, long time."

Dr Ron Cutler, an infectious diseases expert from the University of East London, said: "Continual protection would be a tremendous advantage against flu."

He cautioned however, that there is no guarantee that the M2 protein will not mutate in the future - meaning the jab will have to be regularly reformulated.