Frequency distribution of the reactivity to one or more PfEMP1-varO domain as by groups of healthy adults (HA) and children recruited in 2006 (AP, UM or SM as indicated) and by Ig assay as indicated (total IgG for HA; total IgG, IgG1 and IgG3 for AP, UM and SM). Reactivity was assessed by ELISA on individual domain as indicated in the Methods section. A plasma sample was classified as seropositive when the recorded signal was above the threshold. Seroreactivity to 1, 2 or 3 domains is indicated irrespective of the actual domain recognized in each class. Symbols used for bars: no domain recognized (white), any one domain recognized (grey), two domains recognized (hatched), all three domains recognized (black).