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Basic considerations concerning field trials of malaria vaccines in human populations.

Studies in animals have shown that effective immunity can be induced by vaccines employing plasmodial sporozoites, asexual blood forms (e.g., merozoites), and sexual blood forms (gametocytes/gametes). In the future, but only when extensive safety testing has shown them suitable for administration to human subjects, the efficacy of such vaccines in the control of malaria in human populations will need to be assessed. Field trials will pose many complex problems and assessment of the results they yield will demand precise and detailed information first on the frequency, density of parasitaemia, and clinical severity of malarial episodes in vaccinated and control subjects and second, on the changes that occur in the gametocyte reservoir and entomological indices of transmission within the trial area. They will require to be sited in areas where the prevalence, importance and epidemiology of malaria is known with precision and where much additional information on the endemicity of non-malarial illnesses is available. Trials will entail close collaboration with experienced statisticians and meticulous planning, with special emphasis on the design of an efficient records system. The services of experienced clinicians skilled in the diagnosis and treatment of malarial and non-malarial illnesses will also be essential. Surveillance of the indices of malaria transmission will require competent entomological expertise.