Early Results of an Experimental Malaria Vaccine Hold Promise

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British scientists report they have developed an experimental vaccine that shows early potential to neutralize many, perhaps all, strains of the deadliest malaria parasite.

Preliminary findings in animal tests of the vaccine found that it stopped every strain of Plasmodium falciparum, the parasite that is responsible for 9 out of 10 malaria deaths, that scientists pitted against it in the lab.

The new research, published in Nature Communications, by a team of scientists at the University of Oxford, shores up that team’s previous findings on what it calls the malaria parasite’s “Achilles’ heel”: a protein, or antigen, known as RH5.

In November, the scientists published research showing that P. falciparum relies on RH5 to invade red blood cells, where it replicates and spreads. It attaches the antigen to a single receptor on the surface of human red blood cells, which allows it to unlock the doorway into cell.

Blocking RH5 could stop the parasite from gaining entry into host cells, and keep malaria from developing, the researchers surmised, which is exactly what the experimental vaccine appeared to do. In the animal tests, the vaccine triggered an antibody response that dispatched every strain of the P. falciparum parasite scientists introduced.

Scientists have long sought to develop a vaccine against malaria, but were thwarted by the wiliness of the malaria parasites’ antigens, the target of vaccines. The antigens tend to be extremely genetically diverse because they’re constantly evolving to evade the body’s immune system. “The RH5 antigen doesn’t show this diversity, making it a particularly good target for a vaccine to exploit,” explained Adrian Hill, a Wellcome Trust senior investigator at the University of Oxford, in a statement. “Our next step will be to begin safety tests of this vaccine. If these prove successful, we could see clinical trials in patients beginning within the next two to three years.”

In October, scientists working with GlaxoSmithKline (GSK) Biologicals, the PATH Malaria Vaccine Initiative and the Bill and Melinda Gates Foundation tested a different malaria vaccine — called RTS,S — for the first time in children at 11 sites in Africa. The results were encouraging: RTS,S cut the risk of infection with malaria by 56%, and reduced severe cases of the disease by 47%.

“That’s remarkable when you consider that there has never been a successful vaccine against a human parasite, nor against malaria,” said Dr. Tsiri Agbenyega, head of the malaria research unit at the Komfo-Anokye Hospital in Ghana and chair of the RTS,S Clinical Trials Partnership Committee, at the time.

Still, in order to eradicate malaria, scientists say a much more powerful vaccine is needed. By comparison, other vaccines that children receive against childhood infections, such as measles and rotavirus, reach efficacy rates of 70% to more than 90%.

Simon Draper of Oxford’s Jenner Institute, who worked on the current study, suggested the possibility of using the RH5 vaccine, which targets the malaria parasite in the blood, to complement RTS,S, which stops P. falciparum from entering the liver, another crucial stage of the parasite’s life cycle in the body. “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,” Draper told Reuters.

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