Why a malaria vaccine?
The RTS,S vaccine against malaria featured in a Times article today is the closest to possible licensure and use, but it's not the only malaria vaccine candidate. Studies on several others that have also advanced to human trials were presented Monday at a meeting of the American Society of Tropical Medicine and Hygiene underway in New Orleans.
One, under development by the U.S. Naval Medical Research Center and the biopharmaceutical company GenVec Inc., is a genetic vaccine, a newer technology than the protein-based RTS,S. It uses genes found in the DNA of the malaria parasite and delivers them via a de-activated cold virus, prompting the production of antibodies as well as another type of immune reaction called a cell-mediated response.
Another, from the U.S. Military Vaccine Program and the biotech firm Sanaria Inc., is a vaccine that uses an injection of live but weakened malaria parasites to provoke an immune response, much like the measles or mumps vaccines do.
More than one type of vaccine may be needed to beat back malaria, according to Dr. Carlos C. "Kent" Campbell, a longtime director of the malaria program at the national Centers for Disease Control and Prevention. The mosquito-borne parasite that causes malaria is wily. Like HIV, the AIDS-causing virus, it mutates and evades the immune system.
Like many parasites, Plasmodium falciparum also has a complex life cycle, existing in different stages in the liver and bloodstream, making it difficult to target. There is, in fact, no licensed vaccine against any human parasitic disease. Decades of failures have fueled considerable skepticism among malaria experts about whether a vaccine is even possible.
What is not in dispute is that a malaria vaccine is needed, even with the impressive success of insecticide-treated bed nets over the last two years. Campbell pointed out that only one class of insecticide now exists to treat bed nets. So when mosquitoes develop resistance -- and they inevitably will -- gains such as the impressive 69% reduction in severe malaria cases that Zambian health officials announced at this conference could disappear.
Malaria researchers are passionate advocates of vaccines -- especially when confronted with the vocal vaccine critics that have arisen after a controversial paper, since refuted in numerous scientific studies, suggested that the measles vaccine could cause autism. Today's article on RTS,S, for example, has generated e-mail accusations that African children are being used as guinea pigs.
The original guinea pigs were volunteers like Dr. Thomas L. Richie, a U.S. Navy captain who directs the naval research center's malaria program. He and fellow researchers, along with White House policy wonks, doctors from the National Institutes of Health and other volunteers, not only received the first innoculations but agreed to be stung by malaria-carrying mosquitoes to see whether the vaccine worked.
"Vaccines are always accepted when the horror of the disease is in front of us," Richie said. "We grew up not seeing measles, never seeing diphtheria."
In the early 1900s, he said, diphtheria swept through New England towns, killing a quarter of grade-school-age children within two weeks. The horror of malaria is still very much at the front in sub-Saharan Africa, where 90% of the estimated 1 million deaths occur each year, most of them among children under age 5.
-- Mary Engel