Abstract From 2003 through 2009, 687 of 2885 patients (23.8%) treated for Plasmodium falciparum malaria in clinical studies in Myanmar or on the Thailand-Myanmar border had recurrent Plasmodium vivax malaria within 63 days, compared with 18 of 429 patients (4.2%) from 2010 onward (risk ratio RR, 0.176; 95% confidence interval, .112–.278; P < .0001). Corresponding data from 42 days of follow-up revealed that 820 of 3883 patients (21.1%) had recurrent P. vivax malaria before 2010, compared with 22 of 886 (2.5%) from 2010 onward (RR, 0.117; 95% CI, .077–.177; P < .0001). This 6-fold reduction suggests a recent decline in P. vivax transmission intensity and, thus, a substantial reduction in the proportion of individuals harboring hypnozoites. Before 2010, 687 of 2885 patients treated for Plasmodium falciparum malaria in Myanmar had recurrent Plasmodium vivax malaria within 63 days, compared with 18 of 429 from 2010 onward. This 6-fold reduction suggests a recent substantial decline in P. vivax transmission and consequent hypnozoite carriage.