One unsung success of the 21st century has been the fight against malaria. In 2000 the disease killed 47 people per 100,000 of those at risk. In 2015, the most recent year for which figures are available, that had dropped to 19—a fall of 60%. Even so, malaria kills 430,000 people each year. Some 70% of those who succumb are children under five.
In 2018, this infanticidal bias may begin to change. The coming year will see the widespread testing of the first effective vaccine against Plasmodium falciparum, the parasite that causes the most deadly type of malaria. The vaccine, called RTS,S, will be given exclusively to children. It has been under development since 2001 by a collaboration between Glaxo SmithKline, a British drug company, and PATH, an American global-health charity.
Making a malaria vaccine is hard. Theapproach employed for vaccines against viruses and bacteria—using attenuated or killed examples of the pathogen in question—does not work for Plasmodium. This is a creature far more complex than a bacterium or virus, even though it is single celled. So the body’s immune system must be directed by the vaccine towards an appropriate weak spot in the parasite’s armour, rather than being made to attack the whole thing.
The inventors of RTS,S have discovered such a chink: a particular protein found in malarial sporozoites. The sporozoite is the stage of the parasite’s life cycle that forms in a mosquito’s salivary glands and is then injected into a victim’s bloodstream when that mosquito feeds. Sporozoites circulate until they reach the liver, where they lodge, proliferate and turn into the next stage of the life cycle, merozoites. Catching the parasite at the sporozoite stage nips any infection in the bud. Injection of a vaccine containing a version of the protein in question, which can be produced in bulk in a laboratory, primes the immune system to recognise and attack that protein, killing the sporozoite it is attached to.
Although the deployment of RTS,S in 2018—in Ghana, Kenya and Malawi—will only be a pilot scheme intended to test the vaccine’s effectiveness in the rough and tumble of African clinical life, it will be a big one. The Malaria Vaccine Implementation Programme, as it is known, will recruit 360,000 children, aged between five months and 17 months, to receive a series of four doses of RTS,S. A similar number of other children, matched for age and circumstances, will be observed without vaccination, in order that comparisons can be made. The programme will be run by the World Health Organisation and the bills paid by three transnational health initiatives, Gavi, the Global Fund and Unitaid.
The auspices are reckoned to be good. In the biggest previous trial of RTS,S, which ended in 2014, the rate of infection in children receiving it was around 40% lower than it was in the unvaccinated group. That, statisticians reckon, translates into a saving of one child’s life per 200 vaccinated.
Persuading parents to bring their children to a clinic for four successive shots, which may not coincide with the existing regimen of childhood vaccines, could prove an obstacle. Nor will RTS,S, even if it is as successful as its supporters hope, be enough to knock malaria on the head. But, added to bed nets, insecticides and the judicious deployment of drugs, it would bring further pressure to bear on the disease, and would keep the death toll coming down for years to come.
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