The world’s best hope for a malaria vaccine is still on track, with news this week that the RTS,S/AS02D vaccine appeared to cut severe disease by 58% among young Mozambican children.
The researchers also reported that new infections of malaria among the one- to four-year-olds vaccinated appeared to be reduced by 65% — but warned that this figure should be treated with caution.
The RTS,S/AS02D trial is partially funded by the Path Malaria Vaccine Initiative, working with pharmaceutical company GlaxoSmithKline. Lead researcher Pedro Alonso, a professor at the University of Barcelona, said the trial not only confirmed the safety of the vaccine, but also indicated it was effective. If this effectiveness is confirmed in large-scale stage-three trials, the vaccine could be licensed for use on young children within four years.
Announcing the results in The Lancet, the researchers said the vaccine had proved to be ‘safe, well tolerated and highly immunogenic [causes a strong immune response] in young infantsâ€.
But bad news comes with the announcement by the United Nations’ agency for children, Unicef, that malaria-related mortality among children in Africa is not falling. While countries were phasing out ineffective anti-malarial drugs in line with World Health Organisation guidelines, they had not yet replaced them with the more effective and expensive combination drugs, Unicef said.
Each year more than 800Â 000 African children are thought to die from the disease before they reach the age of five. Only a third of children with malaria receive treatment, and only 2% to 3% access the effective combination drugs.
The new vaccine is meant to postpone new malaria infections in young children, so that when they become infected they are more likely to survive. The scale of malaria-associated deaths means that even partially effective vaccines for children could save thousands of lives each year.
Human malaria is caused by one of four species of Plasmodium, of which the most dangerous is P. falciparum. Up to one in five people not treated after being infected with this parasite will die.
The malaria parasite has a multistage life cycle in the liver, bloodstream and red blood cells of humans, and inside the female mosquitoes that transmit it. In humans it can cause damage to the liver, kidneys and nervous system. Cerebral malaria can kill children within hours.
People in malaria-ridden areas who survive their initial bouts of the disease develop levels of resistance. By the end of their first decade, they may show no signs of the disease even though they are infected — although they act as a reservoir for the parasite. This natural immunity falls away when they move to non-malaria areas and they are no longer repeatedly exposed to the disease.
RTS,S/AS02D was first created in 1987 by fusing proteins from P. falciparum with those from hepatitis B. The vaccine induces an immune response that helps prevent the parasite from infecting the liver.
The use of a vaccine such as RTS,S/AS02D would be part of a layered strategy against the disease, accompanying initiatives to provide insecticide-treated bed nets and sprays to combat the mosquitoes.