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Experimental malaria vaccine shows early promise

British scientists have developed an experimental malaria vaccine that may have the potential to neutralize all strains of the most deadly species of malaria parasite.

Results from very early tests of the vaccine in mice and rabbits show it induces an antibody response able to halt many strains of the P. falciparum parasite, the form that causes almost all of the 655,000 malaria deaths worldwide each year.

The researchers, whose work was published in the journal Nature Communications on Tuesday, plan to take the vaccine into early stage human trials in two to three years, but it may be a decade or more beyond that before it is fully developed.

"Vaccines against malaria are notoriously difficult to develop," said Adrian Hill of Britain's Oxford University, who worked on the vaccine research team.

This vaccine builds on work published last month by the same team, who pinpointed a single receptor for a protein called RH5 that is critical for the malaria parasite to gain entry into red blood cells where it multiplies and spreads.

The researchers said in November they thought that by blocking this process, they could halt the disease in its tracks - and Tuesday's results confirm their thinking.

"What's exciting about RH5 is that we've shown that antibodies against this protein have so far knocked down every parasite we've been able to test in the laboratory," Simon Draper of Oxford's Jenner Institute, who also worked on the study, said in a telephone interview.

"We haven't found one yet that the vaccine isn't able to stop."

Malaria is a mosquito-borne parasitic disease that killed around 655,000 in 2010 according to latest World Health Organisation data. The vast majority of malaria deaths are among children and babies in sub-Saharan Africa.

The blood stage of the parasite's life cycle begins when it invades human red blood cells, and it is this stage that is responsible for malaria illnesses and deaths.

Scientists have been working for decades on trying to develop an effective vaccine against the disease, but this has proved particularly tricky because the parasites' antigens - the target of vaccines - tend to be genetically too diverse.

Researchers say RH5 doesn't show this diversity, making it a particularly good target for a vaccine to exploit.

British drugmaker GlaxoSmithKline published data in October showing its experimental vaccine, RTS,S, halved the risk of children getting malaria in a large trial in Africa, making it likely to become the world's first licensed malaria vaccine.

Other teams of researchers around the world are also working on other approaches to a malaria vaccine.

Experts agree that wiping out the disease - a goal the scientific community says could be achieved in the next few decades with the right tools - will need a vaccine that is more effective than RTS,S.

"Unlike RTS,S, which aims to stop the parasite getting into the liver, this RH5 vaccine is trying to kill the parasite in the blood," Draper explained. "So it may be possible that the RH5 vaccine could complement RTS,S."

"Ultimately we don't know until we test our vaccine in humans whether it will be more efficacious than RTS,S. But these data on RH5 are some of the most exciting in the field at the moment."

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