RTS, S is thought to reduce the risk of infection from each exposure, rather than conferring" all or nothing" protection on a proportion of recipients. 5 By this hypothesis, everyone vaccinated will eventually experience malaria if transmission is high enough. 5 In other words, the vaccine should have a greater effect on the incidence rate of the first or total episodes of clinical malaria than on the overall proportion of people experiencing it, a conclusion supported by the phase III data. 2 Although analysis of hazard and incidence rate ratios is valid, 5 the risk ratio for clinical malaria provides additional relevant information to policy makers and parents of immunised children and should also be reported. First results of phase 3 trial of RTS, S/AS01 malaria vaccine in African children.