Total, AMA1-specific and non-AMA1 IgG preparations Total IgGs were purified from individual plasma samples from the U.S. trial (n = 5) and normal U.S. sera (n = 2) using Protein G columns as described previously [14] . Similarly, total IgG was prepared from each plasma sample collected on Days 0 and 42 from the Mali Phase 2 trial. All of the total IgGs were dialyzed against RPMI 1640 and concentrated to 40 mg/ml. Because the volume of the total IgG from each individual Malian child was not enough to perform AMA1-specific IgG purification, the total IgG samples were ranked based on their anti-AMA1(3D7) antibody level as judged by ELISA and were divided into 3 or 4 groups to make pooled IgGs at each time point as follows: For Day 0 IgGs (regardless of immunization groups), D0-1, D0-2, D0-3 and D0-4; for Day 42 IgGs from HiberixH-vaccinated children, Hib-1, Hib-2 and Hib-3; for Day 42 IgGs from AMA1-vaccinated children, AMA1-1, AMA1-2 and AMA1-3. The number of individual total IgGs used to make each total IgG pool and the antibody level of the pool is shown in Table 1 . Although all of the anti-malarial antibody in Day 0 IgGs and Day 42 IgGs from the Hiberix group was induced by natural infection, it is possible that vaccination with HiberixH and/or the timing of blood collection during the malaria transmission season might alter the immune response. Therefore, we made separate pooled IgGs from Day 0 IgGs and Day 42 IgGs from HiberixH group in this study.