Since the first vaccine, when Edward Jenner in England used an extract of cow pox to prevent small pox, vaccines have become a part of most people’s life. Many millions of people have received a vaccine of some kind – in most cases, many different vaccines. The vaccination programmes against small pox, polio, tetanus and diphtheria have made these once-common diseases virtually unknown in the developed world. In the case of type 1 diabetes, although not strictly a ‘vaccine’, preventive treatments have been successful in animal models. Colin Dayan reports on the progress being made in work to develop an injection to prevent against type 1 diabetes in people.