Consistent Safety and Infectivity in Sporozoite Challenge Model of Plasmodium vivax in Malaria-Naive Human Volunteers

1Limited succes of classic malaria control measures has prompted the search for vaccines and because of the epidemiological importance of P. falciparum , which is responsible for ~80% of the malaria cases globally, greater efforts have been invested in this parasite species than in P. vivax. However, progress is also being achieved in the development of P. vivax subunit vaccines. Two candidates, one based on the circumsporozoite (CS) protein and another based on the oocyst/ookinete Pv s25 protein, have been tested in phase I clinical trials. 2– 4 Recent phase I clinical trials conducted using different formulations of P. vivax CS-derived subunit vaccines based on long synthetic peptides (LSP) have indicated that such formulations are safe, well tolerated, and immunogenic in malaria-naive volunteers. Additionally, an Escherichia coli recombinant chimeric full-length molecule of the P. vivax CS has also been recently reported. Sera from individuals naturally exposed to malaria in endemic areas and from immunized mice displayed high antibody titers to the recombinant protein. This construct is also being considered as a vaccine candidate and being proposed for further clinical trials. 5 During the last few years we have been developing a P. vivax challenge model because assessing the protective efficacy of P. vivax malaria vaccines requires a safe, reliable, and reproducible method of infecting human volunteers with sporozoites.