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BackgroundIn the Greater Mekong Subregion of Southeast Asia, Plasmodium vivax malaria is endemic and causes significant morbidity. In this study, the efficacy of chloroquine for treating uncomplicated P. vivax malaria at the eastern and western borders of Myanmar was investigated.MethodsA total of 197 participants with microscopically confirmed P. vivax infection were enrolled from three townships of the southeastern (Thanbyuzayat and Kawthoung) and western (Kyauktaw) borders of Myanmar. Patients were treated with chloroquine according to the national malaria treatment guidelines and followed for 28 days.ResultsAmong the 197 enrollments, 172 completed the 28-day follow-up. Twelve recurrent P. vivax infections, all occurring in the third and fourth week, were detected, resulting in an overall cumulative rate of recurrence of 4.7% [95% confidence interval (CI) 1.5-7.8]. The incidence rate of recurrence varied among the three sites. In Thanbyuzayat township, no patients had recurrent parasitemia between days 7 and 28. In contrast, Kyauktaw township had a day 28 cumulative incidence rate of recurrence of 7.2% (95% CI 0.6-13.9%) compared to 6.9% (95% CI 0.6-13.2) in Kawthoung township.ConclusionWhile this study confirmed the relatively high clinical efficacy of chloroquine for treating P. vivax in Myanmar with modest rates of recurrent infections within 28 days of the treatment, it also revealed considerable geographical heterogeneity of chloroquine efficacy, which warrants continuous surveillance efforts.