A vaccine against the bacteria Group A streptococcus (‘strep’) could prevent common minor infections like sore throat and school sores as well as deadly ones like necrotising fasciitis (‘flesh eating disease’). It would also reduce long-term heart (rheumatic heart disease) and kidney problems. We are going to try and deliberately give a sore throat to adult volunteers under very close medical supervision so that we can learn more about immunity to strep and to help make and test new vaccines.