London, A universal flu vaccine, which could mean an end to the annual jab, is being tested on volunteers in Britain, BBC reported.

If successful, the vaccine developed by Oxford University researchers would also be a key weapon against flu pandemics.

Experts said such a vaccine was the "holy grail" for flu researchers but there was still a long way to go.

Study leader Sarah Gilbert said traditional influenza vaccines are designed to prompt an immune response to H and N proteins on the outer shell of the virus.

But these proteins are prone to mutation - and every year the vaccine has to be reformulated on the basis of the strains likely to be most prominent.

So, the researchers have developed a vaccine on the basis of proteins inside the cell, which are far more similar across different strains.

The new vaccine uses a weakened smallpox virus to carry the proteins into the body - a technique that has already been used in malaria and TB vaccines.

Once the virus has invaded the cell and starts to multiply, these inner proteins called matrix protein 1 and nucleo-protein are revealed to the immune system.

A specific type of immune cell, called a T cell, then learns to recognise and destroy cells containing the proteins the next time it encounters them.

Initially 12 people will be vaccinated to test the dose before further studies are done to check its effectiveness in people exposed to flu.

New universal flu vaccine is injected into the arm and is taken up by healthy cells.

Gilbert said if they were successful it could drastically change the way flu vaccine is used.

"With having to make a new vaccine every year there's never enough to go around. With this vaccine, we could end up having everyone vaccinated - a situation more like measles where you don't really see it anymore," the researcher said.

In the case of a pandemic, stockpiles of the vaccine could be made in advance instead of having to wait for an outbreak to then identify the particular strain of flu.

John Oxford, a flu vaccine expert at Queen Mary, University of London said such a vaccine would be the "ultimate prize".

"But it's a fairly difficult prize to get - it may just be a question of luck."

He added that having to manufacture different flu vaccines every year was a "huge burden" on pharmaceutical companies.

"This team has experience with this type of vaccine so they may well get there."

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