Phase IIa/b Trial of PvCS/Montanide ISA-51 Malaria Vaccine in Adults in Chocó, Colombia

Plain-language summary

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.

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