To investigate the potential importance of IgM alongside IgG in protection from malaria, we measured IgM and IgG levels in plasma samples against intact merozoites in 199 children (5 to 14 years old) from a longitudinal cohort in a moderate-to-high malaria transmission region of PNG (17); all children were treated to clear parasitemia at enrolment and then monitored by active surveillance for parasitemia and clinical malaria over 6 months of follow-up. Here, CD40LG is linked to malaria.