A new vaccine that may offer lifetime protection against the flu has shown promise in human trials. It works on the deadly type A strain, responsible for pandemics. Current flu vaccines work by giving immunity against two proteins, called haemagglutinin and neurominidase, found on the surface of flu viruses. However, as these proteins continually mutate, vaccines have to be reformulated every year to keep on working. The new vaccine, known as ACAM-FLU-A, gets around this problem by homing in on a protein called M2, found on all type A strains, that does not mutate so readily. The vaccine could be quickly produced in response to a flu outbreak. The doses can be mass produced and used at any time, because there is no need to identify the most prevalent strains. In theory, a single injection could offer lifetime protection. Whether this will work in practice is a matter for future trials.