People who recover from swine flu may be left with an extraordinary natural ability to fight off flu viruses, findings suggests.
In beating a bout of H1N1 the body makes antibodies that can kill many other flu strains, a study in the Journal of Experimental Medicine shows.
Doctors hope to harness this power to make a universal flu vaccine that would protect against any type of influenza.
Ultimately this could replace the "best guess" flu vaccines currently used.
Such a vaccine is the "holy grail" for flu researchers. Many scientists are already testing different prototypes to put an end to the yearly race to predict coming flu strains and quickly mass produce a new vaccine each flu season.
Dr Patrick Wilson who led the latest research said the H1N1 swine flu virus that reached pandemic levels infecting an estimated 60 million people last year, had provided a unique opportunity for researchers.
"It demonstrates how to make a single vaccine that could potentially provide immunity to all influenza.
"The surprise was that such a very different influenza strain, as opposed to the most common strains, could lead us to something so widely applicable."
In the nine patients they studied who had caught swine flu during the pandemic, they found the infection had triggered the production of a wide range of antibodies that are only very rarely seen after seasonal flu infections or flu vaccination.
Five antibodies isolated by the team could fight all the seasonal H1N1 flu strains from the last decade, the devastating "Spanish flu" strain from 1918 which killed up to 50m people, plus a potentially deadly bird flu H5N1 strain.
The researchers believe the "extraordinarily" powerful antibodies were created as the body learned how to fight the new infection with swine flu using its old memory of how to fight off other flu viruses.
Next they plan to examine the immune response of people who were vaccinated against last year's swine flu but did not get sick to see if they too have the same super immunity to flu.
Dr Sarah Gilbert is a expert in viruses at Oxford University and has been testing her own prototype universal flu vaccine.
She said: "Many scientists are working to develop a vaccine that would protect against the many strains of flu virus.
"This work gives us more confidence that it will be possible to generate a universal flu vaccine."
But she said it would take many years for a product to go through the necessary tests and trials.
"It will take at least five years before anything like this could be widely available."
The number of deaths this winter from flu verified by the Health Protection Agency currently is 50, with 45 of these due to swine flu.