Plasmodium Vivax Malaria

Tafenoquine was recently approved by regulatory authorities in the USA and Australia. Tafenoquine is an alternative radical curative treatment to primaquine acting against the dormant liver stage of Plasmodium vivax (the hypnozoite). Tafenoquine (an 8-aminoquinoline) has the substantial advantage of single dosing as compared to a 14-day course of primaquine to achieve radical cure. The recommended tafenoquine dose is 300 mg, which was shown to be significantly worse in radical curative efficacy to a total primaquine dose of 3.5 mg/kg in Southeast Asia. The cure rate of tafenoquine 300 mg in Southeast Asian study sites was only 74%. The comparator 3.5 mg/kg total primaquine dose is the standard and most commonly used dose globally, but in Southeast Asia and the Western Pacific, higher doses of primaquine are needed for radical cure. This study aims to determine the optimal dose of tafenoquine in Southeast Asia. Addendum for Indonesia: The INSPECTOR trial results showed that tafenoquine 300mg was not efficacious for radical cure (79% probability for recurrence after treatment). The comparator arm, low-dose primaquine 3.5mg/kg divided equally over 14 days, showed a 48% probability of recurrence after treatment). The standard of care for radical cure in Indonesia is high-dose primaquine 7mg/kg divided in 7 daily doses).

FLAME is an open-label cluster-randomized controlled trial that aims to determine the effectiveness of focal mass drug administration (fMDA) to reduce the incidence of Plasmodium vivax malaria in the Loreto Department in Peru. Standard interventions, including symptomatic and asymptomatic screening for malaria infections, provision of insecticide-treated bednets, and environmental transmission monitoring, will be compared to clusters of villages randomized to receive anti-malarial drugs.

This clinical study will evaluate an investigational malaria vaccine called PvCS/Montanide ISA-51 to determine whether it is safe and whether it can protect adults from infection with Plasmodium vivax, one of the main parasites that causes malaria. P. vivax malaria is common in tropical regions, including Colombia, and can lead to recurrent fever, anemia, and prolonged illness. Currently, no licensed vaccine effectively prevents P. vivax infection. The investigational vaccine (PvCS) contains synthetic peptides derived from the circumsporozoite (CS) protein located on the surface of P. vivax sporozoites. The vaccine is formulated with the adjuvant Montanide ISA-51 to enhance the immune response. This study aims to assess the safety of the PvCS/Montanide ISA-51 formulation and to determine whether it can prevent malaria after controlled exposure to the parasite. This is a Phase IIa/b, randomized, double-blind, placebo-controlled clinical trial conducted by the Malaria Vaccine and Drug Development Center (MVDC/CIV) in collaboration with ASOCLINIC IPS and the Pacific Health Institute (INSALPA) in Quibdó, Chocó, Colombia. A total of 72 healthy adults aged 18-50 years from malaria-endemic areas will participate. Participants will be randomly assigned in a 2:1 ratio to receive either the PvCS/Montanide ISA-51 vaccine or a placebo. The study product will be administered by intramuscular injection at months 0, 2, and 4. After each vaccination, participants will be monitored for side effects and provide blood samples to measure immune responses, including antibody levels and T-cell activity. Approximately one month after the third vaccination, participants will undergo a controlled human malaria infection (CHMI), during which they will be exposed to P. vivax through the bite of infected mosquitoes under strict medical supervision. Following exposure, participants will be monitored daily using blood tests to detect malaria at the earliest stage. If malaria parasites are detected-or if 21 days pass without infection-participants will receive prompt, effective antimalarial treatment based on Colombian national guidelines. All participants will continue to be followed for up to 12 months after the challenge to ensure safety and assess long-term outcomes. Primary goals of the study include: Determining whether the PvCS/Montanide ISA-51 vaccine prevents P. vivax infection after CHMI. Measuring the time between exposure and first detection of parasites (pre-patent period). Evaluating the safety and tolerability of the vaccine. Secondary goals include: Measuring immune responses generated by the vaccine. Exploring relationships between immune responses and protection from infection. The total duration of the study is expected to be approximately 30 months, including recruitment, immunizations, challenge procedures, and follow-up. Results will help determine whether this vaccine can safely protect adults against P. vivax malaria and guide planning for future larger-scale vaccine trials in endemic populations.

In this area of Greater Mekong Subregion (GMS), vivax malaria is the most common kind of malaria. It can stay very long in the liver, and come out later to make another episode of illness. This can happen many times even without a mosquito bite. Only 8-aminoquinoline drugs can kill the liver forms of the malaria parasite. One of these drugs is called primaquine, and it has been used all over the world for a long time. There is now a new formulation of this 8-aminoquinoline drug called tafenoquine that can also treat the malaria in the liver. The main benefit of this drug is that it is a single dose, which makes much convenient for the patients as well as for the malaria control program than conventional 14 days of primaquine. Recent research suggests that ACT (Artemisinin Combination Therapy) may antagonise the efficacy of tafenoquine (Baird et al. 2020 ASTMH Annual Meeting) . This could prevent the use of tafenoquine in areas with chloroquine resistant P. vivax parasites where national malaria programmes recommend ACTs for vivax malaria. Also, currently recommended tafenoquine dose is sub-optimal: 300 mg dose proved significantly inferior to low dose primaquine in a meta-analysis of the phase 3 studies when restricted to the Southeast Asian region (Llanos-Cuentas et al. 2019 NEJM; Watson et al. 2022a Elife). A tafenoquine dose of 450mg is predicted to provide \>90% of the maximal effect. The objective of this research is to find out whether 450 mg dose of tafenoquine can be combined effectively with ACT providing a short course treatment for P. vivax malaria.