Malaria is a mosquito-borne infectious disease that causes high fevers, shaking chills, and flu-like symptoms. It also kills more than 1 million people globally each year. Four different kinds of malaria parasites infect humans, including one called Plasmodium vivax. However, Plasmodium vivax malaria is hard to treat, in part because it can remain dormant for weeks or months, only to rear its head long after initial infection.

Now, researchers from Walter Reed Army Institute of Research (WRAIR) report that they’ve developed a new vaccine candidate for Plasmodium vivax along with GlaxoSmithKline, a British pharmaceutical company. The research, published in the journal PLOS Neglected Tropical Diseases, is reportedly the first in-human study of its kind.

Researchers injected 30 human volunteers (who had all been bitten by malaria-infected mosquitos) with three doses of the vaccine. Then, they looked at blood smears to see whether the individuals developed malaria, or if the malaria parasites took longer to appear in their blood.

While the vaccine didn’t prevent malaria infection, it reportedly produced “robust immune responses” among human subjects and delayed parasitemia, or the presence of parasites in the blood, by 59 percent. Scientists hope that these results might someday lead to an effective vaccine.

“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," Lt. Col. Robert Paris, M.D., director of the U.S. Military Malaria Research Program at WRAIR, said in a release. "Vaccines and antimalarial drugs are both critical needs for the DoD to protect service members from malaria."

[h/t Science Daily]