October 15, 2004 Malaria Vaccine Proves Effective By DONALD G. McNEIL Jr. For the first time, researchers say, a vaccine against malaria has shown that it can save children from infection or death.
The vaccine, tested on thousands of children in Mozambique, was hardly perfect: It protected them from catching the disease only about 30 percent of the time and prevented it from becoming life-threatening only about 58 percent of the time. But because malaria kills more than a million people a year, 700,000 of them children, even partial protection would be a public health victory. The disease, caused by a parasite carried by mosquitoes, is found in 90 countries, and drug-resistant strains are spreading. Dr. Allan Schapira, strategy coordinator for the Roll Back Malaria campaign at the World Health Organization, said the trial was "good news, and definitely of great interest for malaria control." The director of the Malaria Vaccine Initiative, which is underwriting tests on 15 experimental vaccines with money from the Bill and Melinda Gates Foundation, said the GlaxoSmithKline product tried in Mozambique was now its leading candidate and had proved that the concept worked. "We'd all like to see the numbers be higher, absolutely," said Dr. Melinda Moree, director of the initiative. "But these are still very significant findings." The results - to be published tomorrow in the British medical journal The Lancet - were comparable to or better than other methods of preventing infection in African villages, like distributing mosquito nets and insecticides, she said. A malaria expert not connected with the study, Dr. Dyann Wirth, director of the Harvard Malaria Initiative, a program at the Harvard School of Public Health that is also seeking cures, was more cautious. She said the findings opened "a fruitful area for further investigation," but needed larger trials. Glaxo and the Malaria Vaccine Initiative are planning such trials. But experts said it would be several years before the vaccine could be adopted as a childhood inoculation like those for diphtheria or measles. It is not yet known how long the vaccine's protection lasts, whether it is safe for infants and whether it is compatible with other vaccines. A trial of the same vaccine among adults in Gambia six years ago showed that it protected about 35 percent of them from infection, but that the protection waned after about two months. Still, experts noted that children stand to benefit more from a vaccine. In rural Africa, people can be infected several times a year. Children who survive to adulthood become immune. Newborns inherit some protection from their mothers, but it wears off in a few months. Young children are the hardest hit, and many who survive are brain-damaged. The most recent vaccine test, conducted in two rural districts in southern Mozambique, where malaria is endemic during the six-month rainy season, involved 2,022 children ages 1 to 4. Half of them were given the malaria vaccine; rather than placebos, the other half got vaccines against hepatitis or bacteria that cause meningitis. To ensure that the results were not skewed by other factors, the control and vaccine groups had roughly equal numbers of children who slept under mosquito nets at home and who lived near a clinic. The children were followed for six months and had home visits with blood and temperature checks at least once a month. Those who developed malaria were given immediate medical attention; the disease can kill in as little as 48 hours, but it can be cured if it is caught in time. To test the vaccine's ability to prevent new infections, two subgroups of about 180 children each were given drugs to clear any parasites they might have had before the trial began. In both subgroups, most children developed new parasites. But the number was considerably smaller among those who had received the vaccine: 123 children in the vaccine group, compared with 159 in the control group. Over all, 11 vaccinated children developed severe malaria while 26 in the control group did. Fifteen children died of various causes. None in the vaccine group died of malaria, while four in the control group did. Those numbers are too small to have any statistical meaning. Mozambique is one of the world's poorest countries, where 200 out of every 1,000 children die before age 5, said Dr. Regina Rabinovich, director of infectious diseases for the Gates foundation, so the death rate across the whole study was lower than normal, presumably because the children in it got better than average medical care. The trial was conducted by the biologicals division at Glaxo and the Mozambique Ministry of Health, with financing from the Malaria Vaccine Initiative, which was created in 1999 with $50 million from the Gates foundation. Malaria is spreading - possibly, some experts say, because global warming has encouraged the spread of mosquitoes. More people die of the disease today than did 30 years ago. Beyond death and retardation, there are economic consequences. For example, families affected by malaria harvest only 40 percent of the crops of healthy ones, according to the World Health Organization. A malaria vaccine, one of the holy grails of tropical medicine, has proved surprisingly elusive. Health authorities have been fighting malaria since the Panama Canal was a gleam in Theodore Roosevelt's eye. Until the Gates foundation arrived, work on vaccines for tropical diseases had languished for decades because they make little profit for drug companies. (The world spends about $400 billion a year on drugs, but only about $8 billion on vaccines.) The American military, which also does malaria research, had limited amounts of money for it. The Glaxo vaccine, known as RTS,S/AS02A, has been in development and testing for 17 years, said Dr. Joe Cohen, one of its inventors. It fuses a bit of hepatitis B virus with a bit of the falciparum strain of the parasite, which is the most common, and usually the most deadly, form of malaria. The piece of the parasite is from the life stage that is injected by mosquitoes, so antibodies and white blood cells stimulated by the vaccine attack before the parasite can settle in the liver and reproduce. Pieces of the hepatitis virus were added because they provoke strong immune responses, Dr. Cohen said. (Another malaria vaccine candidate uses a weakened version of a smallpox vaccine to do the same.) The goal, he said, is to create immunity that lasts longer than natural immunity, which fades in adults after they move out of malaria areas. Dr. Rabinovich of the Gates foundation said future vaccines might incorporate proteins from other parts of the parasite's life cycle. But she added: "This demonstrates that vaccines have the potential to prevent millions of child deaths. That's something to wake your mom up about." http://www.nytimes.com/2004/10/15/health/15malaria.html?ei=5094&en=4c048f53ba2eed48&hp=&ex=1097899200&partner=homepage&pagewanted=print&position= --- URG-L Pour quitter URG-L, envoyez un message a la liste ([EMAIL PROTECTED]) avec, COMME SUJET, le mot REMOVE (rien d'autre).
