Based on practical and statistical considerations the researchers proposed to enroll 40 volunteers per group (a total of 120). Allowing for a steady rate of drop-out during follow up amounting to total of 20% of subjects by the end of the trial, the trial has at least 80% power to detect a difference in time to infection between the malaria vaccine and rabies groups, if the vaccine efficacy is at least 60%, and at least 70% of the control group volunteers develop detected parasitaemia during the trial.