Malaria vaccine test gives cautious hope

Results in Africa point to breakthrough

November 30, 1999|By Douglas Birch | Douglas Birch,Sun Staff

WASHINGTON -- An experimental malaria vaccine achieved limited success in a field trial in West Africa, researchers said yesterday, fueling cautious hopes that people can one day be inoculated against one of the planet's most prolific killers.

The vaccine briefly reduced malaria cases by almost two-thirds in a group of volunteers in Gambia last year, researchers said. Scientists disclosed the results yesterday at a meeting of the American Society of Tropical Medicine and Hygiene here.

"I think it's a great step forward," said Dr. Philip K. Russell of the Center for Immunization Research at the Johns Hopkins School of Public Health. "We've got, for the first time, protection against malaria in the wild, even if it's only short-term."

Scientists recruited 306 men in six rural villages in Gambia, a nation about 200 miles long and about 12 miles wide, lying inside Senegal. After two months, almost two-thirds were protected, but that rate fell to just 16 percent after 15 weeks. It was too short a time for a practical vaccine.

But researchers were heartened yesterday about the results. "This gives encouragement to everyone in the field," said Dr. Robert Edelman, a malaria vaccine researcher at the University of Maryland. "We need successes."

The vaccine, developed by the Walter Reed Army Institute of Research and SmithKline Beecham, protected about half of volunteers in a series of small-scale trials in the institute's Washington labs over the past three years. But the African trial tested the vaccine against different strains of the malaria parasite in an area of intense transmission.

"People just assumed this would be another in a long line of failed vaccines," said Dr. Kent E. Kester of Walter Reed. "When the results were unsealed, we were very excited."

The vaccine consists of a piece of the malaria parasite linked to a piece of the hepatitis B virus, and mixed with a cocktail of compounds called adjuvants, meant to boost the response of the immune system. Like all vaccines, the Walter Reed-SmithKline product is designed to teach the immune system to respond quickly and aggressively to a particular microbe.

Researchers cautioned that the vaccine isn't ready for clinical use. "The Gambia trial confirmed the good and bad things about the vaccine," says Dr. W. Ripley Ballou, until recently the leader of the Walter Reed effort. "Yes, it confers immunity on about half the people it's given to. But it lasts only a couple of months. Nobody believes that we have a vaccine that is ready for licensing or that will meet sub-Saharan Africa's needs."

Still, Ballou and others hope that the product, called RTS,S, can become the foundation of a practical vaccine.

Dr. Stephen L. Hoffman of the Naval Medical Research Institute says he plans in January to use RTS,S to "boost" a vaccine developed in his labs. Hoffman's vaccine works by inserting malaria genes into the DNA of human muscle cells, causing those cells to make chemical structures normally made only by the parasite. Released into the bloodstream, those chemical structures stimulate the immune system, preparing it for combat with the parasite itself.

Eradicated in industrialized countries in the 1940s, malaria is

common throughout the tropics -- especially among the rural poor. It ranks with tuberculosis and AIDS as one of the biggest killers among infectious diseases. The World Health Organization estimates that each year the mosquito-borne parasite causes a half-billion cases of clinical illness and 1 million to 2 million deaths.

Scientists have sought a malaria vaccine since 1880, when a French doctor in Algiers first identified the malaria microbe in the blood of a soldier. Malaria is a parasite, an animal with complex tactics for evading the human immune system. While there are many vaccines against bacterial and viral illnesses, no one has ever made a workable vaccine against a parasite.

Over the past century, malaria has wrought enormous casualties upon U.S. soldiers in tropical battlefields. Malaria was the second leading cause of hospitalizations for U.S. troops in Vietnam, after combat wounds. Almost a third of American soldiers in Somalia were hospitalized with the disease.

The Pentagon aims for a vaccine that would, at minimum, shield 80 percent of troops for six months. Such a vaccine could also be sold commercially to tourists and other travelers to the tropics. Scientists at Walter Reed and SmithKline say they want to protect the billions of people living in malaria endemic areas. To be practical, such a "civilian" vaccine would have to last at least several years.

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