British scientists have edged closer to developing a "holy grail" universal influenza vaccine that would tackle all strains of the illness.
Researchers at Imperial College London (ICL) have drawn on the results of a study into the 2009 swine flu pandemic, which found those with more virus-killing immune cells in their blood at the start of the pandemic avoided severe illness.
They believe a vaccine that stimulates the body to produce more of these cells - known as CD8 Ts - could be effective at preventing flu viruses, including new strains that cross into humans from birds and pigs, from causing serious disease.
Professor Ajit Lalvani from the National Heart and Lung Institute at ICL, who led the study, said: "New strains of flu are continuously emerging, some of which are deadly, and so the holy grail is to create a universal vaccine that would be effective against all strains of flu."
Influenza kills between 250,000 and 500,000 globally per year, according to the World Health Organisation.
The ICL announcement comes after scientists in America said they thought they might have developed "universal" protection against the killer virus.
Speaking in May, the US researchers said the vaccine was created by a team working for US healthcare company Sanofi using techniques that have also raised hopes of a new generation of vaccines against other diseases.
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Prof Lalvani's team recruited 342 staff and students at Imperial to take part in their study in autumn 2009, following the outbreak of the flu.
Volunteers donated blood samples and were given nasal swabs, supplying regular updated information about their health.
Researchers found those who fell more severely ill with flu had fewer CD8 T cells in their blood, and those who caught flu but had no symptoms or only mild symptoms had more of these cells.
Prof Lalvani said: "Our findings suggest that by making the body produce more of this specific type of CD8 T cell, you can protect people against symptomatic illness. This provides the blueprint for developing a universal flu vaccine.
"We already know how to stimulate the immune system to make CD8 T cells by vaccination.
"Now that we know these T cells may protect, we can design a vaccine to prevent people getting symptoms and transmitting infection to others.
"This could curb seasonal flu annually and protect people against future pandemics."