FRIDAY, Dec. 7, 2001 (HealthDayNews) -- An experimental malaria vaccine may head off the deadly parasite before it takes hold in red blood cells, say researchers in Africa who are testing the shot.
The vaccine, called RTS,S/AS02, shields people exposed to the mosquito-borne pathogen and seems to be the first such vaccine to offer significant protection, says a report on the findings in tomorrow's issue of The Lancet.
Malaria is the world's deadliest infection. It kills three people a minute, more than 4,000 a day and roughly 1.5 million a year, mostly children in Africa, experts say.
The disease is caused by a quartet of parasites, most notably Plasmodium falciparum, which are passed to people through the bite of infected mosquitoes. Each year, from 300 million to 500 million people contract the illness; 40 percent of the world's population lives in areas where the disease is endemic.
Researchers are working on many types of malaria vaccines, targeting the parasite at various stages of its life cycle. The vaccine in the African trial, which is made by Belgium-based GlaxoSmithKline Biologicals, consists of a protein fragment of P. falciparum fused to a protein taken from the surface of the hepatitis B virus. Attaching it to the virus enhances its ability to trigger an immune response. Because the combination blocks the parasite from entering red blood cells, it is called a pre-erythrocytic vaccine.
In one part of the study, Kalifa Bojang, with colleagues from the U.K. Medical Research Council Laboratories, tested the vaccine in 306 Gambian men, ages 18 to 45, at the start of malaria season.
The men were put in two groups: some were given three doses of the injection; a comparison, or control group received three doses of a rabies vaccine. All the men also were given supplementary treatment with sulfadoxine/pyrimethamine, a commonly used malaria treatment, two weeks before the third dose.
Over the next 15 weeks, the men who got the malaria vaccine developed the disease later than those who received the rabies injections. While, overall, about one in three men didn't contract malaria, the shots were about twice as effective during the study's first nine weeks.
In an experiment a year later, the researchers gave 73 men the three-dose malaria vaccine plus a fourth dose and followed them for nine weeks. This time, the addition of the booster provided somewhat more protection. Again, the vaccine was most effective in the early going, but the researchers don't really know why. Encouragingly, the shots seemed to protect men against not only P. falciparum but other malaria-causing organisms, as well.
The vaccine proved relatively safe, causing headache, pain at the site of the shot and malaise but few major side effects, the researchers say.
Dr. Regina Rabinovich, director of the Malaria Vaccine Initiative (MVI), in Rockville, Md., calls the latest results "the first hint that you can generate an immune response" to ward off infection in adults living amid the parasite.
However, her group is more concerned with how well the shot will work in children, whose immune systems aren't used to the parasites and who, as a consequence, bear the brunt of malaria's devastation. Children under age 5 make up 75 percent of the malaria deaths each year, she says.
Earlier this year, MVI and Glaxo began first-stage trials of the vaccine in children ages 6 to 12, and will expand the trial next year to younger children in Mozambique.
The World Health Organization and community leaders in Africa have said that a malaria vaccine that shields half the children who receive it from disease and death would be welcome, and some have suggested that a vaccine with even 30 percent to 50 percent protection would be acceptable, Rabinovich says.
Dr. Lee Hall, who directs malaria vaccine research at the National Institute of Allergy and Infectious Diseases, says the latest work confirms an important proof-of-concept study with the inoculation several years ago. But the looming question is: "Are you going to be able to move this down into the target populations that have the greatest burden of disease -- that is, young children."
In addition to the pre-erythrocytic vaccine, Hall is helping coordinate studies with compounds that attack malaria parasites in their blood and sexual stages, which could help control its symptoms and transmission, respectively. Clinical trials with these vaccines should begin sometime next year, he says.
What To Do
For more on the global threat of malaria, visit the World Health Organization or the MVI.
For more about malaria and how to avoid it while traveling to endemic areas, try the Centers for Disease Control and Prevention.
You can also check this deluxe site from the Bill and Melinda Gates Foundation, but, be warned, it's a heavy download.
