CYP2D6 and Plasmodium vivax malaria: These findings suggest that the excess of relapses among people with severely reduced CYP2D6 activity adds relatively little to the overall burden of vivax malaria episodes.<h4>Conclusion</h4>Amazonians with an AS ≤ 0.25, but not necessarily those with intermediate CYP2D6 activity, have a greater risk of recurrence after a PQ-treated P. vivax infection and require alternative relapse suppression regimens for the radical cure of vivax malaria.