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ROBERT SIEGEL, HOST:

This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.

MELISSA BLOCK, HOST:

And I'm Melissa Block. First this hour, a landmark in public health. Researchers say they have solid evidence that an experimental vaccine against malaria works. A study of 6,000 children across Africa shows the vaccine cuts the chances of getting malaria by more than half. As NPR's Richard Knox reports, the results are fueling talk of eradicating a disease that kills hundreds of thousands of people each year.

RICHARD KNOX, BYLINE: This is the first time malaria vaccine developers can really claim they're onto something that might make a difference. Dr. Tsiri Agbenyega of Ghana, one of 140 authors of today's study, spoke about the results at a big malaria conference in Seattle.

DR. TSIRI AGBENYEGA: This is remarkable when you consider that there has never been a successful vaccine against a human parasite, nor obviously against malaria.

KNOX: It's hard enough to make a good vaccine against the bacterium or a virus. Those are simple targets compared to the malaria parasite. It morphs into many different forms as it cycles from mosquitoes to humans and back again. And surviving malaria doesn't mean you can't get it again. In the study, researchers found that kids who didn't get the vaccine got malaria on average one and a half times a year. In fact, for every 1,000 kids who did not get the new vaccine, there were 1,500 cases of malaria.

DR. CHRISTIAN LOUCQ: If those kids had received the vaccine, those kids had only 750 cases of malaria, a reduction by half.

KNOX: That's Dr. Christian Loucq of PATH Malaria Vaccine Initiative. He led the new study, which is published online by the New England Journal of Medicine. Loucq says the vaccine also cut the risk of the most serious cases of malaria.

LOUCQ: So that means in fact we reduce the chances to die from malaria by half.

KNOX: But a vaccine that cuts the risk of sickness and death by half is much less effective than vaccines against polio, measles, pneumonia or other diseases. They typically prevent infection around 90 percent of the time. One official at the Bill and Melinda Gates Foundation, which has put $200 million into the new vaccine, said she didn't know if it will be considered good enough to give to hundreds of millions of children. But authors of the new study were less cautious.

DR. PATRICIA NJUGUNA: I think most parents would be happy to have 50 percent less cases.

KNOX: That's Dr. Patricia Njuguna, a Kenyan researcher.

NJUGUNA: So if you can even reduce the multiple episodes in that child to one or none, that would be a big relief to a mother rather than having multiple episodes of malaria.

KNOX: And others point out that malaria is such a big problem that a less-than-ideal vaccine could still make a huge difference. Half the world's population is threatened by malaria. Nearly a quarter of a billion people get infected every year, and almost 800,000 die, most of them children under 5 in Africa. But the decision on whether to launch a malaria vaccine is complicated. Nobody knows how long its protection will last or how much it will cost. Most vaccines for the developing world cost pennies a dose. One of the most expensive, for pneumonia, costs three-and-a-half dollars a dose. Dr. Andrew Witty, head of GlaxoSmithKline, told reporters today that the company will keep this vaccine affordable.

DR. ANDREW WITTY: Our intention is to supply this vaccine at the lowest price possible. We have no intention of making a profit here.

KNOX: The new vaccine comes at a time of optimism about rolling back malaria. Deaths have already been cut by 20 percent over the past few years. Professor Dyann Wirth of Harvard says this has been accomplished with relatively low-tech measures - bed nets to keep mosquitoes from biting, insecticide sprays, prompt diagnosis and treatment.

DR. DYANN WIRTH: If you were keeping score, you know, malaria, public health community, well, I would say malaria is still winning, but there are some battles where actually the public health community is doing better than it was previously.

KNOX: Some are saying that adding even a partially effective vaccine could make eradication of malaria possible. Bill and Melinda Gates proposed that back in 2007.

WIRTH: In their lifetime, it's possible. I mean, we're thinking this is a 40- or 50-year task.

KNOX: That would put it around the year 2060. Richard Knox, NPR News.

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