Experimental Malaria Vaccine Shows Promise In Human Test

Aug 8, 2013
Originally published on August 9, 2013 10:02 am

A viable, effective vaccine against malaria has long eluded scientists. Results from a preliminary study have ignited hope that a new type of vaccine could change that.

The experimental vaccine offered strong protection against malaria when given at high doses, scientists report Thursday in the journal Science.

The study was extremely small and short-term. And the candidate vaccine still has a long way to go before it could be used in the developing world.

Nevertheless, Dr. Anthony Fauci, who leads the National Institute of Allergies and Infectious Diseases, calls the findings unprecedented.

The vaccine, called PfSPZ, protected 12 of the 15 volunteers from malaria, including all six who received the high dose. By contrast, 11 of the 12 participants who weren't vaccinated came down with malaria.

"It's true to say that this is really impressive to have this degree of protection," Fauci says about the results. "But on the other hand you have to temper it by saying the numbers are still relatively small."

The trial needs to be replicated on a far larger scale, he says. And it's still unknown how long the malaria protection lasts.

The participants in this study were all bitten by five mosquitoes infected with the malaria parasite Plasmodium falciparum three weeks after getting the vaccine shot.

Because everyone got exposed at the same time, this study wasn't designed to show how PfSPZ works over time. For any vaccine to be successful in the field, it would need to ward off the disease for years after the inoculation. Three weeks would be way too short.

Previous experimental vaccines have shown some effectiveness against the malaria parasite, but none have provided high levels of protection against the disease. In November, another candidate vaccine showed disappointing results in tests among young infants, though it provided children moderate protection against the parasite.

PfSPZ is different from these previous vaccines because it uses whole, weakened parasites to trigger an immune response, instead of just a small part of the parasite, like a protein on its surface.

"We don't have any vaccines against parasitic infections like malaria because the parasite is so complex. It changes itself in your body. It morphs from one stage to the next," says Stephen Hoffman, the CEO of the Rockville, Md., company Sanaria, which developed PfSPZ.

Specially, PfSPZ gets certain immune cells, called T cells, to attack the parasite directly, instead of relying primarily on an antibody response.

"The idea that somehow one is going to make a vaccine that just attacks one of those thousands of proteins, and that's going to provide long-term protective immunity has always seemed odd to me," he says. "But that's what all the other approaches are about."

Sanaria is moving quickly to conduct larger scale trials of PfSPZ in Africa. A study in Tanzania is slated to start in six weeks.

If things go well with the upcoming trials, Hoffman says, the earliest the vaccine might be available for widespread use would be in late 2017 or early 2018.

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Malaria is one of the most devastating diseases in the developing world, but it has no viable, effective vaccine. Today, researchers are announcing a new vaccine that blocks malaria when given at high doses.

NPR's Jason Beaubien reports that based on one early laboratory trial, there's optimism about this new prospect. But it still has a long way to go before it can be used effectively worldwide.

JASON BEAUBIEN, BYLINE: According to the World Health Organization, there were roughly 220 million cases of malaria in 2010, almost all of them occurring in the poorest nations on Earth. The pounding fever makes many people unable to walk, never mind work. And in Africa alone, malaria claims hundreds of thousands of lives each year. For decades, finding an effective malaria vaccine has been the holy grail of tropical medicine.

DR. ANTHONY FAUCI: Parasites like malaria have been really very confounding in our ability to develop very good vaccines that are highly effective.

BEAUBIEN: Dr. Anthony Fauci is the head of the National Institute of Allergies and Infectious Diseases at the National Institutes of Health. He says the results of a phase one clinical trial of the new vaccine, which are being published today by Science magazine, are quite impressive. Phase one studies generally test whether a new drug or product is safe. This trial, however, showed that this vaccine was not only safe, but among the six people given a full dose, it completely protected them against malaria.

FAUCI: That's very good, and in some respects, it's true to say it's unprecedented. But you have to immediately say remember, that number is a rather small number. Six is a small number.

BEAUBIEN: Fauci says the vaccine is going to have to be tested on a much larger scale, and he says there are still many questions about whether it can provide long-term protection against malaria. This vaccine is different from earlier attempts at a malaria vaccine in that it functions by getting certain immune cells to attack the parasite directly rather than by creating a traditional anti-body response.

STEPHEN HOFFMAN: What we are doing is very different from what's happened before, and I was involved with what's happened before for many, many years.

BEAUBIEN: Stephen Hoffman is the CEO of the Rockville, Maryland, company Sanaria, which developed the inoculation. He says rather than try to isolate one part of the malaria parasite and get the human body to develop a defense against it, his new vaccine uses a weakened form of the entire parasite as the vaccine.

HOFFMAN: We have demonstrated, for the first time in the history of malaria, that one can completely protect individuals against malaria-infected mosquitoes.

BEAUBIEN: One drawback of the new vaccine is that it has to be injected intravenously, making it complicated for mass campaigns. Field tests will also have to see how well it responds to different strains of the parasite. Nevertheless, an official from the World Health Organization's Malaria Control Program in Geneva calls the results released today interesting and an important scientific achievement. Sanaria is moving quickly to conduct larger scale trials of the product in Africa. A study in Tanzania is slated to start in just six weeks. Hoffman at Sanaria says if things go well with the upcoming trials, the vaccine may be available for widespread use by late 2017 or early 2018.

Jason Beaubien, NPR News, Washington. Transcript provided by NPR, Copyright NPR.