Resistance to artemisinin-based vaccine combination therapies, the most effective treatments for malaria has been reported at the border between Cambodia and Thailand. The World Health Organization (WHO) insists immediate action must be taken to prevent a catastrophe. Meanwhile, a leading vaccine has shown in studies to protect children in Africa at least 15 months of solid protection after being administered.
An artemisinin resistant parasite emerged in areas along the Cambodia-Thailand border in mid 2000, and is suspected of having spread to other areas in Cambodia, Myanmar, Thailand and Vietnam. WHO has since initiated an aggressive containment plan in the affected locations.
Artemisinin also known as qinghaosu, and its derivatives are a group of drugs that possess the most rapid action of all current drugs against falciparum malaria. Treatments containing an artemisinin derivative (artemisinin-combination therapies, ACTs) are now standard treatment worldwide for falciparum malaria.
WHO Director General Margaret Chan states regarding the program’s launch that took place this past Wednesday in Switzerland:
“The usefulness of our most potent weapon in treating malaria is now under threat. The new plan takes advantage of an unprecedented opportunity in the history of malaria control: to stop the emergence of drug resistance at its source and prevent further international spread.”
Five thousand miles away, the lead candidate malaria vaccine (RTS,S/AS01E) provides young African children with sustained protection against malaria for at least 15 months after vaccination, making it a very promising public-health intervention with the potential to save hundreds of thousands of lives, according to an Article published Online First in The Lancet Infectious Diseases.
Malaria kills nearly 900,000 people a year in Africa, mainly young children under the age of five. In 2008, initial results showed that the RTS,S/AS01E vaccine gave 53% protection against clinical malaria for at least 8 months. Today it is reported that after 15 months, children vaccinated with RTS,S/AS01E were 45.8% less likely to be infected with the P falciparum parasite.
The RTS,S/AS01E vaccine works by attacking the malaria parasite in its early stages when it first enters the bloodstream or liver cells. It then attempts to completely prevent infection of red blood cells (erythrocytes) and the development of serious symptoms.
Between March 2007 and October 2008, 894 children aged 5 to 17 months from Kenya and Tanzania were randomly assigned to three doses of either RTS,S/AS01E or rabies vaccine. Blood samples were taken before vaccination and at regular intervals during the trial to test for antibodies.
Ally Olotu from the Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya, and colleagues state:
“RTS,S/AS01E confers sustained efficacy for at least 15 months and shows promise as a potential public health intervention against childhood malaria in malaria endemic countries. Further studies are needed to establish vaccine efficacy in, for example, children with HIV infection or those who are malnourished. Furthermore, phase 3 studies should include study sites at different transmission intensities to confirm how generalisable our results are.”
Malaria transmission can be reduced by preventing mosquito bites by distribution of inexpensive mosquito nets and insect repellents, or by mosquito-control measures such as spraying insecticides inside houses and draining standing water where mosquitoes lay their eggs. Although many are under development, the challenge of producing a widely available vaccine that provides a high level of protection for a sustained period is still to be met.
Brian Greenwood from the London School of Hygiene and Tropical Medicine, London, UK, discusses how the lack of an immunological measurement to reliably predict protection against malaria infection has hindered vaccine development:
“The need for such a correlate will become less if the [ongoing] phase 3 trial of the RTS,S/AS01 confirms the promise shown in…[this] study done in Kenya and Tanzania, and RTS,S/AS01 becomes the first malaria vaccine to be licensed and widely deployed.”
Authors:
Dr Ally Olotu, Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
Or Justa Wawira, Communications Officer, Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
Professor Brian Greenwood, London School of Hygiene and Tropical Medicine, London, UK.
Source:
Written by Sy Kraft, B.A.