A new malaria vaccine candidate has been found to generate robust immune response while significantly delaying arasitemia in 59 per cent of vaccinated subjects, according to a first-of-its-kind in-human study.
Plasmodium vivax malaria is challenging to control because it can be dormant, causing no symptoms, and then become active causing symptomatic malaria weeks to months after initial infection. The vaccine candidate, developed by researchers at Walter Reed Army Institute of Research (WRAIR) in the US and tested jointly with GlaxoSmithKline (GSK) to prevent vivax malaria infection, is the first in-human study of its kind under an investigational new drug application with the US Food and Drug Administration.
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WRAIR researchers immunised 30 volunteers with three doses of the vaccine candidate. Immunised volunteers took part in WRAIR’s well-established controlled human malaria infection (CHMI) model where they were bitten by malaria-infected mosquitoes. The efficacy of the vaccine candidate was then determined based on whether or not volunteers developed malaria by looking at blood smears or if it took longer for malaria parasites to appear in the blood.
“This study represents the first vaccine study to test the effectiveness of a P vivax vaccine candidate in humans using controlled human malaria infection,” said Jason W Bennett, the study’s lead investigator. Unlike P falciparum where a CHMI model is well established, the P vivax CHMI model must rely on blood donations from infected humans to initiate infections in mosquitoes. The vaccine candidate was well tolerated in all volunteers and generated robust immune responses. While the vaccine candidate did not prevent malaria infection, it did significantly delay parasitemia in 59 per cent of vaccinated subjects.
Parasitemia is used as a measurement of parasite load in the organism and an indication of the degree of an active parasitic infection. Robert Paris, director of the US Military Malaria Research Programme at WRAIR, said that an improved vaccine can be designed. “Findings from the analysis of the immune response of vaccinated subjects have given us clues to improve vaccine candidates and studies are now underway at WRAIR to develop next generation vivax vaccines,” said Paris.
Researchers were also able to demonstrate that individuals with low or absent levels of a specific liver enzyme were unable to convert primaquine, the only FDA-approved drug to treat the dormant stages of vivax malaria, to an active drug form to kill the dormant stage of
the parasites. The findings were published in the journal PLOS Neglected Tropical Diseases.