Whooping cough, known as pertussis, is a serious infection, especially in infants. Two types of pertussis vaccine exist: whole-cell (wP) and acellular (aP). We now think that aP vaccines may not be as long-lasting or effective in preventing infection as wP vaccines, but the cause remains unknown. It may be due to differences in specific groups of cells in the immune system called T-helper cells. The type of T-helper cells found in animals and humans who have received wP- compared to aP-vaccines is better at preventing bacteria from being passed on. We still do not know enough about all the important T-helper cells involved and there is no data in very young children. My project is set within a larger study in The Gambia that is vaccinating babies with aP or wP vaccine. I will investigate T-helper cells activated by these vaccines and see how they may help other components of the infant’s immune system. As well as taking blood samples, I will collect and analyse fluid from the infant’s nose (where pertussis bacteria initially infect), to provide further insight into how these vaccines differ in their action. My findings will help to design better pertussis vaccines in the future.