In order to evaluate the immune response to these vaccines we will be measuring not only the blood levels of antibodies specific to serogroup A, C, W−135 and Y meningococci, but also the population of white blood cells known as B cells which produce these antibodies. Two forms of these B cells will be measured, the plasma cells (which actively produce antibodies) and memory B cells (which do not produce antibodies but persist in the body and can be stimulated to turn into plasma cells when required).