We fitted time-to-event data from cohort participants who experienced vivax malaria, using Cox proportional hazards models, to explore how genotype-determined CYP2D6 activity, expressed as activity scores (AS), modulates the risk of P. vivax recurrence within 6 months after treatment with chloroquine and PQ (total dose, 3.5 mg/kg). The gene discussed is CYP2D6; the disease is Plasmodium vivax malaria.