Researchers in the first-of-its-kind study at the US’sWalter Reed Army Institute of Research (WRAIR) developed a new malaria vaccine to produce robust immune response even though it could not altogether prevent infection.
However, it significantly delayed parasitemia in 59% of the vaccinated patients, the research findings revealed. Plasmodium vivax malaria is not easy to control as it can lie dormant showing no symptoms and then unexpectedly become active causing symptomatic malaria a couple of weeks or months after initial infection.
The vaccine candidate developed recently was tested jointly with GlaxoSmithKline (GSK) to avoid the infection of vivax malaria under an investigational new drug application with the US Food and Drug Administration
Researchers at WRAIR vaccinated 30 volunteers with three dosages of the vaccine. Vaccinated candidates participated in WRAIR’s well-founded, regulated human malaria infection (CHMI) model where they were bitten off by mosquitoes infected with malaria.
The effectiveness of the vaccine was then established based on whether or not volunteers succumbed to malaria by closely observing blood smears or if malaria parasites took a longer time to spread in the blood.
The study’s lead investigator, Jason W Bennett, said that the research findings symbolize a first-of-its-kind vaccine study to determine the efficacy of a P vivax vaccine among humans by means of controlled human malaria infection. Not like P falciparum where a CHMI model is well-founded, the P vivax CHMI model must seek blood donations from humans who are infected so as to initiate infections in mosquitoes.
All volunteers very well tolerated the vaccine and produced favorable immune responses. Whereas the vaccine could not put off malaria infection; it significantly postponed parasitemia in 59 percent of the immunized subjects.
Parasitemia is used to determine parasite load in the organism, which also indicates the degree of an active parasitic infection. Director at the US Military Malaria Research Program at WRAIR, Robert Paris said that a better vaccine can be developed and results from the study of the immune response of immunized volunteers have given signs to improve vaccine and research is now in progress at WRAIR to design next generation vivax vaccines.
Researchers could also show that the subjects with absent or low levels of a specific liver enzyme were not able to convert the only FDA-approved drug called primaquine, to cure the dormant stages of vivax malaria, to an active form of drugs in order to destroy stages of the parasites.
The research study was published in the PLOS Neglected Tropical Diseases Journal.