Scientists in america say they've made a major breakthrough in designing a vaccine against all known strains of flu. 0ur medical editor, fergus walsh, is here. we are locked in a perpetual war against the constantly changing flu virus. every year scientists have to make an educated guess as to which strains will be circulating. this winter's flu vaccine protects against four strains of flu including h1n1 which triggered the swine flu pandemic and h3n2 — the most common strain globally. now, scientists in the united states have developed a vaccine against all 20 known a and b strains. the vac...