Malaria Vaccine Effective in Latest Trials

MONDAY Dec. 8, 2008 Results from two phase II trials in Africa show that a new malaria vaccine is effective at preventing both infection and the mosquito-borne disease itself in infants and children.

"Malaria is killing almost 1 million people, mostly African children, every year," Dr. Christian Loucq, director of the PATH Malaria Vaccine Initiative, said during a morning teleconference Monday. "Clearly, the world needs a safe and effective malaria vaccine."

The vaccine, called RTS,S, is one of several vaccine candidates for malaria, Loucq said. Other vaccines are under development, but RTS,S is the one that is furthest along and ready for phase III testing, he noted.

"These studies offer further evidence that RTS,S provides both infants and young children with substantial protection against the disease," Loucq said. "We are closer than ever before to having a malaria vaccine for use by the children in Africa."

The findings were published online Dec. 8 in the New England Journal of Medicine.

RTS,S was developed by drugmaker Glaxo-Smith-Kline. When the shot is given it also has another component, called either ASO1 or ASO2, which is given to boost the vaccine's effectiveness.

In one study, 340 Tanzanian infants under 1 year old received the RTS,S/ASO2 vaccine along with other vaccines for diphtheria, tetanus, pertussis and heamophilus influenzae B.

"There was a 65 percent reduction in first infection from malaria in those infants who received three doses of the vaccine and were followed over a six-month period," said lead researcher Dr. Salim Abdulla, head of the Bagamoyo Research and Training Centre of the Ifakara Health Institute, in Tanzania. "A safe and efficacious malaria vaccine for children in Africa may be available in the near future and have the potential of alleviating a huge burden of malaria disease," he added.

The researchers also found that RTS,S/ASO2 could be safely and effectively given along with other childhood vaccines. The malaria vaccine did not interfere with the protective responses of other vaccines. And the effectiveness of the RTS,S malaria vaccine wasn't compromised by the other vaccines, Abdulla said.

In the second study, 894 children in Kenya and Tanzania, ages 5 to 17 months, were given either three doses of the malaria vaccine or a rabies vaccine. The researchers found a 53 percent reduction in the risk of developing malaria among children who received the RTS,S vaccine.

"If these findings were replicated in a Phase III multi-center study, we would expect that study to lead to an application for a license for RTS,S/AS01 as a vaccine to prevent clinical malaria," said lead researcher Philip Bejon, of the Kenya Medical Research Institute (KEMRI)-Wellcome Collaborative Research Programme and the Centre for Tropical Medicine at the University of Oxford, in England.

"The vaccine would be only partially effective, but may still be a useful addition to malaria control programs," Bejon added.

The differences in the results of the two trials can be explained by what the researchers were looking for. In the first trial, the scientists looked for the presence of malaria in the infants' blood; in the second trial they looked for children who actually went on to develop the disease.

It's unclear how long the vaccine would be effective. But, in a four-year follow-up of children given the vaccine in Mozambique, the inoculation remained effective in preventing most cases of malaria, Loucq said.

Phase III trials of the vaccine are set to begin early next year, he said.

The vaccine trials were funded by a grant from the Bill & Melinda Gates Foundation to the PATH Malaria Vaccine Initiative, and drug maker GlaxoSmithKline.

Dr. Marc Siegel, an expert in infectious diseases and an associate professor of medicine at New York University School of Medicine, agreed that there was an urgent need for a malaria vaccine.

"Malaria is a huge worldwide problem infecting from 300 to 500 million people a year and killing more than a million worldwide," Siegel said. "In the U.S. we don't give it the attention it deserves. The new vaccine is very exciting, and highly worthy of our attention and support."

Two other reports in the same journal issue looked at the effectiveness of malaria drugs in different parts of the world.

In one report, researchers wanted to see if there were new strains of malaria resistant to artesunate, a common drug used to treat the disease. For the study, 56 people in Cambodia given the anti-malaria drug artesunate responded to treatment, indicating there were no strains of malaria resistant to the drug, the researchers said.

In the second report, 482 children with malaria in Papua New Guinea were randomly assigned to a combination of anti-malaria drugs. The researchers found that the most effective pairing was the combination of artemether-lumefantrine, which had a response rate of 95.2 percent against the malaria strain, called P. falciparum.

And in a report published online Dec. 8 in The Lancet, researchers found that the rectal application of artesunate was effective in treating children with malaria. The rectal application could be important because in severe cases of malaria patients cannot swallow or keep medicine down.

More information

For more on malaria, visit the U.S. Centers for Disease Control and Prevention.

Posted: December 2008


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