A new type of flu drug could prove a potent weapon against resistant strains of the virus, research has shown.

The drug effectively throws a spanner in the works to block the mechanism the virus uses to spread between cells.

In laboratory tests it proved effective against a wide variety of strains, including those resistant to drugs such as Tamiflu.

It also protected mice against lethal influenza infection.

To spread inside the body, the flu virus uses two "entry" and "exit" proteins. One, haemagglutinin, helps it enter and infect a cell. The other, neuraminidase, allows replicated viruses to break out of the cell and move on to the next target.

The new class of drugs sabotages neuraminidase and stops it functioning. As a result the virus becomes "stuck" and unable to continue down the path of infection.

Professor Steve Withers, from the University of British Columbia, who led the research published in the journal Science, said: "Our agent latches onto this enzyme like a broken key stuck in a lock, rendering it useless.

"One of the major challenges of the current flu treatments is that new strains of the flu virus are becoming resistant, leaving us vulnerable to the next pandemic.

"By taking advantage of the virus's own molecular machinery to attach itself, the new drug could remain effective longer, since resistant virus strains cannot arise without destroying their own mechanism for infection."

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