MALARIA VACCINE TRIALS - THE MISSING QUALITATIVE DATA

Recent population-based efficacy trials of the synthetic malaria vacci ne SPf66 have shown restricted, if any, clinical protection against Pl asmodium falciparum infection. Despite the well-established role of an tibodies in effector responses against asexual blood-stage malaria par asites, the titres of anti-SPf66 IgG antibodies do not correlate with the ability of sera from vaccine recipients to inhibit parasite growth in vitro nor with partial clinical protection which could be detected in some trials. Qualitative or functional parameters of SP66-induced antibody responses, such as IgG subclass composition and affinity, may be more predictive of clinical protection against malaria than quanti tative estimates of antibody concentration or titre. Since these param eters are readily estimated by laboratory techniques currently availab le, and may be modulated by changes in vaccination protocols and by th e use of different adjuvants, a better understanding of qualitative an tibody responses induced by SPf66 and other asexual blood-stage malari a vaccine candidates, and of their relationship with clinical protecti on in vivo, is urgently needed for the improvement of currently used i mmunization schedules.