Plasmodium vivax can form dormant liver stages that reactivate weeks or months following an acute infection. Recurrent infections can be associated with a febrile illness, a cumulative risk of severe anaemia, and even mortality. In co-endemic areas the risk of recurrence after both P. vivax and P. falciparum infections can be over 50% within 3 months. The only drug we have to kill P. vivax hypnozoites is primaquine which is currently given as a 14 day regimen. In Papua a retrospective study found very low effectiveness for unsupervised treatment. If true this has profound effects on treatment policy, suggesting that greater efforts are needed to encourage adherence to treatment.