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New malaria vaccine up to 100% effective in early trial - expert comment

Monday, 20 February 2017

A new malaria vaccine has been shown to be 100% effective for at least 10 weeks after the final dose, according to new research published in Nature.

The trials, led by the University of Tübingen, involved immunising 35 people who had never had malaria before with varying doses of the vaccine. The vaccine incorporated live Plasmodium falciparum sporozoites (PfSPZ), cells from the malaria-causing parasite usually injected into the bloodstream after a mosquito’s bite, alongside the antimalarial drug chloroquine.

After the participants were infected with the same strain of malaria, the best response was seen in a group of nine people given the highest dose of the vaccine three times at four-week intervals. At the end of the trial, the nine individuals displayed 100% protection from malaria and displayed no adverse effects.

How novel is this research, and are we now a step closer to having an effective malaria vaccine? Sir Brian Greenwood, Professor of Clinical Tropical Medicine at the London School of Hygiene & Tropical Medicine explains: “Scientists are exploring several different approaches to the development of a malaria vaccine. One of these uses sporozoites, the form of parasite that is injected into the blood when a person is bitten by an infected mosquito. Sporozoites pass quickly to the liver where they develop over the next 10 days without causing any symptoms, before the parasite bursts out into the blood stream and makes the person ill. 

“It has been known for over 40 years that if sporozoites are exposed to x-rays they can still develop in the liver, but no further. Nevertheless, they induce an immune response which protects against malaria. Initially, vaccination was achieved by allowing volunteers to be bitten by hundreds of x-irradiated mosquitoes, a cumbersome approach that would not be practical in the field. More recently it has been shown that protection can also be achieved when purified, irradiated sporozoites are injected with a needle and syringe directly into a vein.

“It has also been shown that live, rather than irradiated, sporozoites can be used if the volunteer is taking the antimalarial drug chloroquine. In this paperthe latter studies have been extended to explore the best combination of dose of sporozoites, number of doses and timing between doses.

“When three injections of a high dose were given at monthly intervals, 9/9 volunteers were protected against malaria 8-10 weeks later.  Further studies of different doses and schedules are planned to shorten the duration of the vaccination procedure. This is a very encouraging set of results and this approach to malaria vaccination is being developed further, first as a means of protecting travellers and the military and then, if all goes well, the population of malaria endemic countries.”

Malaria is one of the deadliest infectious diseases in the world. According to the latest figures from the World Health Organization, 214 million people became infected with malaria in 2015, leading to approximately 438,000 deaths. The authors noted that further investigations and trials are needed to determine if the vaccine could have potential use in mass vaccination strategies and how effective it would be in more diverse populations.

 

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