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.