A super-vaccine that could give permanent protection against all forms of flu is being developed by British doctors.
The once-in-a-lifetime vaccine could do away with the need for an annual jab, according to researchers at Oxford University.
At present, the current jab has to be given every winter to match different circulating strains.
If successful, the new vaccine could be a key weapon against a flu pandemic because stockpiles could be made in advance.
Official estimates of the impact of such a pandemic in Britain show it could lead to 750,000 deaths, with more than six million children affected, including 750,000 under five.
Lead researcher Dr Sarah Gilbert said the vaccine could be used routinely in as little as five years, once tests had been done to ensure its safety and efficacy.
She said a universal vaccine would drastically change the way flu vaccine is used.
'With having to make new vaccine every year, there's never enough to go around,' she said.
'With this vaccine, we could end up having pretty much everyone vaccinated - a situation more like measles, where you don't really need it any more.
'Children would be protected, we'd see economic benefits through reduced sickness in people of working age, and the elderly, who respond less well to vaccination, would be better off through lack of exposure to flu.'
Dr Gilbert added: 'The current approach to influenza vaccination is unsatisfactory for use against seasonal influenza, and of little use when new types of flu begin to infect humans from birds.
'It leaves manufacturers with a few months to produce the necessary stocks, the vaccine has to be administered to at risk populations within a short time window, and those receiving the injection will all have to be vaccinated again the following year.'
The latest approach follows successful tests of another universal vaccine by scientists at Cambridge biotech firm Acambis.
Trials on healthy adults in the U.S. showed the jab is safe, causing no side effects other than the occasional red arm and high temperature associated with all vaccines.
The trials found that after two doses a month apart, it worked fast to prime the immune system to produce antibodies capable of attacking the virus in up to 90 per cent of those tested.
At least two other companies - including British-based biotech firm PepTcell and Swiss developer Cytos - are also working on universal flu vaccines.
The idea behind the universal flu vaccine is to prevent it having to be reformulated every year.
Current vaccines are designed to prompt an immune response to H and N proteins on the outer shell of the virus.
But these proteins change their structure and each year the vaccine has to be reformulated on the basis of the strains likely to be the most prominent.
The Oxford University approach is to develop a vaccine based on proteins inside the cell. These are far more similar across different strains.
The vaccine uses a weakened smallpox virus to carry the proteins into the body, a technique 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.
Those using the vaccine would need to take a booster every five to ten years.
Professor 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. 'There are people trying all kinds of strategies.'
He said the task of manufacturing different flu vaccines every year was a 'huge burden' on pharmaceutical companies. 'This team have experience with this type of vaccine so they may well get there,' he added.
Every year more than 15million people in England alone receive a flu jab in a programme costing £115million.
Priority groups include those aged 65 and over, with around three-quarters of pensioners getting protection each year.
Patients with chronic respiratory disease, heart disease, chronic renal disease and immune system deficiencies can also get jabs on the NHS.