The first-ever Phase III trial for a malaria vaccine has officially begun, with more than 5,000 African children already given the first round of malaria vaccine candidate RTS,S, researchers announced today (November 3) at a pan-African conference on malaria in Nairobi, Kenya.

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"It's a really historical moment," said Joe Cohen, vice president of R&D for Vaccines for Emerging Diseases & HIV at GlaxoSmithKline (GSK) Biologicals and the co-inventor of the vaccine. While the efficacy of RTS,S leaves plenty of room for improvement—providing only about a 50% reduction in malaria—it is the first vaccine candidate for malaria to warrant a Phase III trial.

"It has been an uphill battle to find a vaccine against [malaria]," Cohen said. In Phase II trials, the RTS,S vaccine showed a 53% reduction in clinical episodes of malaria for eight months in children 5 to 17 months old last year, and...

"Of course 53% is not ideal," said malaria vaccine researcher Nirbhay Kumar of the Johns Hopkins Malaria Research Institute, who is not involved in the study. "The world would like to see 80 to 90% efficacy and slightly longer lasting [effects], but clearly the research is moving in a positive direction."

The current trial, now underway in seven African countries, aims to enroll up to 16,000 children in two target age groups: 5 to 17 months and 6 to 12 weeks. The enrollment for the first group is already 5,000 subjects strong, and enrollment of the younger age group is expected to begin in the next couple of weeks, Cohen said. If all goes as planned, the first set of data could be ready to submit for regulatory review in 2012. "We hope that between 3 and 5 years from now we will be able to start the broad implementation of the vaccine," Cohen said. "If this vaccine is implemented in combination with all the other intervention methods," he added, "I think [it] will have a dramatic effect on the burden of malaria and will take us a long way toward eliminating the disease in certain areas in Africa."

RTS,S is the leading vaccine candidate in a global effort coordinated by the PATH Malaria Vaccine Initiative (MVI). Developed by GSK in the late 1980s, the vaccine was first tested in US volunteers in the mid-90s before Phase I/II trials began in Africa in the early part of the new century. RTS,S specifically targets Plasmodium falciparum, the malaria parasite that causes the overwhelming majority of cases of the disease in Africa. Ashley Birkett, MVI's Director of Preclinical Research and Development, said the organization's long-term goal is a vaccine that is at least 80% effective for at least four years. "Now that we have a vaccine that's moving towards licensure we have to take that knowledge and really focus our efforts towards something better," Birkett said. MVI also aims to develop vaccines against P. vivax, a less severe but more widespread malaria parasite, as well as vaccines that block the transmission of malaria to interrupt the life cycle of the parasite. "These transmission blocking vaccines have not received as much attention, [but] they would add an absolutely critical and valuable target" to reduce malaria transmission and ultimately eliminate the disease, said Kumar. "I consider this a very welcome addition to the family of malaria vaccines."

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