Scientists said Monday they had discovered immune cells that can fight all known flu viruses in what was hailed as an "extraordinary breakthrough" that could lead to a universal, one-shot vaccine against the killer disease. Influenza epidemics, largely seasonal, kill hundreds of thousands of people each year, according to the World Health Organization. Due to its mutating strains, vaccine formulas must be regularly updated and only offer limited protection currently. Researchers in Australia said that "killer T cells" - found in over half the world's population - had shown in testing to be effective in fighting all common flu varieties. This means the cells could potentially be used to develop an all-encompassing flu shot that did not need to be changed annually, and even be effective in people who don't naturally possess them.

"Influenza viruses continuously mutate to evade recognition by our immune system, and they are vastly diverse, making it nearly impossible to predict and vaccinate against the strain that will cause the next influenza pandemic," said Marios Koutsakos, a researcher at the University of Melbourne's Doherty Institute.

Copyright Agence France-Presse, 2019