In contrast, while the same AMA1 vaccine increased the anti-AMA1 antibody levels when it was administered to adults who lived in a malaria endemic area, the vaccine did not change the parasite growth-inhibitory activity [15] . In a previous study, we purified total IgGs from sera collected in an epidemiological study in Mali (majority of the sera were collected from adults) and separated the IgGs by affinity chromatography into an AMA1binding fraction (AMA1-specific) or an IgG fraction that does not bind to AMA1 (non-AMA1 IgG). Previously we have shown that the non-AMA1 IgG, more specifically a fraction of the non-AMA1 IgG which can bind to malaria extract, reduced the functional activity of the AMA1 antibodies from U.S. vaccinees [27] . Interference by the non-AMA1 IgG induced by malaria infections likely explains the reason why the AMA1 vaccine did not induce higher growth-inhibitory activity in the Malian adults in the vaccine trial. Because limited volumes of sera were collected from children in the epidemiological study, we could not investigate whether there was such ''interfering'' IgG in the children, who are the main target population of the blood-stage vaccine and who have less previous exposure to malaria.