Quantifying Plasmodium vivax radical cure efficacy: a modelling study integrating clinical trial data and transmission dynamics

Background: Plasmodium vivax forms dormant liver stages (hypnozoites) that can reactivate weeks to months after primary infection. Radical cure requires a combination of antimalarial drugs to kill both the blood-stage and liver-stage parasites. Hypnozoiticidal efficacy of the liver-stage drugs primaquine and tafenoquine cannot be estimated directly because hypnozoites are undetectable. We aimed to estimate hypnozoiticidal efficacy from clinical trial data, and quantify the community-level impact of implementing case management with radical cure. 

Methods: We calibrated a novel P vivax Recurrence Model to publicly available data from prospective clinical trials to estimate the hypnozoiticidal efficacy of different supervised primaquine (3·5 mg/kg or 7 mg/kg over 7 or 14 days) and tafenoquine (5 mg/kg or 7·5 mg/kg single dose) regimens in patients with normal glucose-6-phosphate dehydrogenase (G6PD) activity. We used an existing P vivax Individual-Based Model to quantify the 5-year impact of case management with unsupervised primaquine or tafenoquine regimens across various transmission settings.

Findings: We estimated median hypnozoiticidal efficacies of 99·1% (95% credible interval 96·0–100) for primaquine 7 mg/kg over 14 days; 96·3% (90·8–99·7) for primaquine 7 mg/kg over 7 days; 72·3% (68·1–76·3) for primaquine 3·5 mg/kg over 7 or 14 days; 62·4% (49·1–76·3) for tafenoquine 5 mg/kg single dose; and 87·5% (62·1–99·3) for tafenoquine 7·5 mg/kg single dose. 5 years of community-level tafenoquine case management was estimated to reduce P vivax transmission by 74–79% where pre-intervention prevalence as measured by PCR was low (<2%) and by 17–20% where prevalence as measured by PCR was high (around 35%). Similar 5-year reductions were estimated with primaquine case management only when adherence to the primaquine regimen was above 50%. 

Interpretation: Substantial reductions in prevalence as measured by PCR were predicted with primaquine and tafenoquine regimens if these could be implemented with high coverage and adherence. The benefits of preventing P vivax relapses need to be balanced against the risks of inducing severe haemolysis in patients with G6PD deficiency. Funding: Bill & Melinda Gates Foundation and Horizon Europe.