Preventing relapse in patients diagnosed with P vivax malaria is an essential element of the responsible clinical and public health management of this infection.8 Alternative chemotherapeutic or chemoprophylactic strategies for managing risk of relapse in patients unable to receive or benefit from primaquine therapy (G6PD-unknown patients, G6PD-deficient patients, pregnant women, lactating mothers, young infants, and CYP2D6-impaired patients) have not been conceived, optimized, or validated. This evidence concerns the gene CYP2D6 and infection.