Scientists have found a way to boost an organism's natural anti-virus defences - effectively making its cells immune to flu and other potential killers.
Flu can be a major killer
The process cannot be carried out in human cells - but it could potentially aid the development of effective new anti-viral therapies.
It works by stimulating production of the protein interferon, the cell's first line of defence against viruses.
The study, led by Canada's McGill University, appears in Nature.
The varying forms of the flu virus have killed millions of people down the years, and scientists are concerned that the H5N1 strain of the virus, which currently is overwhelmingly a disease of birds, could mutate to pose a grave threat to human populations across the globe.
Other viruses, such as Sars, have also sparked global health alerts in recent years.
The researchers knocked out two key genes in mice that repress production of interferon.
With these genes out of action, the mouse cells produced much higher levels of interferon, which effectively blocked viruses from reproducing.
Tests on four viruses, including that responsible for flu, produced highly promising results.
Lead researcher Dr Nahum Sonenberg said: "People have been worried for years about potential new viral pandemics, such as avian influenzas.
"If we might now have the means to develop a new therapy to fight flu, the potential is huge."
Dr Mauro Costa-Mattioli, who also worked on the study, said: "In a sense, it is quite a simple story.
"When you get rid of the repressors, you are basically removing the brakes."
The researchers detected no abnormalities or negative side-effects resulting from enhanced interferon production in the mice.
They are optimistic that new drugs can be developed which target the same two key genes in humans.
Professor John Oxford, a virology expert at Queen Mary College School of Medicine, London, said the paper was impressive.
He said: "Boosting the innate immune system seems like a good idea - it has a huge practical application in theory."
But, citing the failed drug trials in North London two years ago which left several young men fighting for their lives, he added: "It could be a double-edged sword.
"You have to be jolly careful that you don't end up on Queer Street."