The long, bumpy path to a malaria vaccine may have hit a smooth stretch as an early-stage study finds that multiple injections with inactivated malaria parasites can protect against the disease.
The findings are tantalizing but preliminary. The study was small, and the vaccine required five intravenously delivered doses to work, which would be an obstacle for teams attempting mass vaccination in developing countries. Also, the shots were tested in adults, not children, who are the prime victims of malaria.
Still, the study offers decidedly good news, says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md., which sponsored the research. “This is an important advance,” he says, noting that the vaccine induces an immune onslaught that kills the malaria parasite in its infective sporozoite stage. That means uninfected mosquitoes that bite a vaccinated person wouldn’t get infected, slowing the disease’s spread, he says.
In the study, researchers gave four or five shots to 15 volunteers over several months. The volunteers were then bitten repeatedly by malarial mosquitoes. A few weeks afterward, 12 showed no disease, including all six who got five doses, the researchers report August 8 in Science. A control group of unvaccinated volunteers got the disease and received treatment promptly.
Scientists already knew that weakened versions of malaria sporozoites could induce immunity in people. To turn the sporozoites into a vaccine, scientists need to irradiate infected mosquitoes, and use the weakened parasites to elicit an immune response in people. In the new study, scientists mastered the delicate task of attenuating the parasites just enough so that they don’t replicate and cause disease, but leaving them active enough to trigger an immune response that would kill any full-strength sporozoites introduced by subsequent mosquito bites. The researchers also effectively delivered the vaccine into volunteers — albeit with IV injections. In earlier tests, this vaccine failed to gin up adequate immunity when given by shots into the skin, which are easier to deliver.
“This is the first step towards success with this approach,” says Denise Doolan, a molecular immunologist at the Queensland Institute of Medical Research in Herston, Australia. “It has taken enormous dedication and perseverance to achieve this result, and [the researchers] should be congratulated.”
Study coauthor Robert Seder, a physician and immunologist at NIAID, says the research team plans to test the vaccine in more people and find out how long the protection lasts. A field trial is planned in Tanzania.
Doolan says simpler and fewer shots are needed for far-reaching vaccination campaigns. If such a vaccine can be developed, she says, it should “have a dramatic impact on public health.”
Meanwhile, Seder says, the IV vaccine — if fully tested and approved — might be useful for protecting health officials, military forces and travelers. Fauci cautions that while this vaccine showed effectiveness against one strain of Plasmodium falciparum, the parasite that causes the most severe kind of malaria, the vaccine will have to prove itself against other strains.
Another experimental malaria vaccine has been shown to be partially protective in children (SN: Online: 10/19/2011).