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The following is a summary of “Quantifying Plasmodium vivax radical cure efficacy: a modelling study integrating clinical trial data and transmission dynamics,” published in the January 2025 issue of Infectious Disease by Ciavarella et al. 

Plasmodium vivax malaria presents a unique challenge due to the presence of dormant liver stages (hypnozoites), requiring radical cure strategies that eliminate both blood-stage and liver-stage parasites. However, the hypnozoiticidal efficacy of current drugs like primaquine and tafenoquine cannot be directly assessed due to the undetectable nature of hypnozoites.  

Researchers conducted a retrospective study to estimate the hypnozoiticidal efficacy using clinical trial data and assess the community-level impact of implementing case management with radical cure.  

They calibrated a novel P. vivax Recurrence Model using publicly available data from clinical trials to estimate hypnozoiticidal efficacy for different primaquine (3.5 mg/kg or 7 mg/kg for 7 or 14 days) and tafenoquine (5 mg/kg or 7.5 mg/kg single dose) regimens in individuals with normal glucose-6-phosphate dehydrogenase (G6PD) activity. They then used an existing P. vivax Individual-Based Model to assess the 5-year impact of unsupervised primaquine or tafenoquine regimens on case management across various transmission settings.  

The results showed that the estimated median hypnozoiticidal efficacies were 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. Community-level tafenoquine case management for 5 years was predicted to reduce P. vivax transmission by 74–79% in low pre-intervention prevalence areas (<2%) and by 17–20% in high prevalence areas (~35%). Similar reductions were seen with primaquine case management when adherence was >50%.  

Investigators concluded that substantial reductions in P.vivax prevalence could be achieved with primaquine and tafenoquine regimens if high coverage and adherence are ensured while acknowledging the need to carefully balance the benefits of preventing relapses against the risk of severe hemolysis in individuals with G6PD deficiency. 

Source: thelancet.com/journals/laninf/article/PIIS1473-3099(24)00689-3/fulltext