Major trials of a vaccine against malaria have provided fresh hope against the scourge that kills an African child every 20 seconds. After showing great promise in Gambia, the vaccine is now being readied for a massive trial next year on children in Mozambique.
鈥淲e鈥檙e very pleased with the results,鈥� says Kalifa Bojang of the British Medical Research Council鈥檚 Gambian laboratories in Banjul, and principle investigator leading the international team that developed and tested the vaccine.
鈥淲e鈥檝e proved it can work under conditions of natural infection, and the next challenge is to try it in children,鈥� he says.
Advertisement
Developed by GlaxoSmithKline, the British-based drugs giant, the vaccine is the first targeted at the so-called 鈥渓iver stage鈥� of the disease.
Cycle of infection
This is when sporozoites of Plasmodium falciparum, the parasite that causes malaria, arrive in the liver from infected blood. After maturing, the parasite remigrates into blood where it can be picked up again by feeding mosquitoes. The mosquitoes then spread the parasite to new victims.
By stamping out the parasite in the liver and blocking its route back into blood, Bojang and his colleagues hope to break the cycle of infection.
Codenamed RTS,S/AS02, the vaccine was fully tested in 131 men. As a 鈥渃ontrol鈥�, 119 others received a rabies vaccine.
Bojang and his colleagues tracked the volunteers for 15 weeks over Gambia鈥檚 peak period of infection, taking blood samples and testing for antibodies to the parasite.
Not spectacular
Overall, they rated the vaccine as 34 per cent effective. 鈥淚t means that each time they are bitten by an infected mosquito, their risk of getting malaria is reduced by a third,鈥� says Bojang.
Bojang agrees that the results are not spectacular. 鈥淔or most infectious diseases, 30 per cent is not good enough and most vaccines are around 70 per cent effective,鈥� he says. 鈥淏ut malaria is such a serious disease that governments may consider using the vaccine anyway.鈥�
He says that the vaccine was 70 per cent effective in the first nine weeks, but tailed off after that. More encouragingly, the efficacy rose again to 47 per cent in 73 men given a booster dose the following season. 鈥淚t means the results are reproducible,鈥� says Bojang.
Fizzled out
There were 20 times as many antibodies to the parasite in vaccinated volunteers. 鈥淭here was correlation between level of antibodies and protection from disease,鈥� says Bojang.
He and his colleagues in Britain, the US and Belgium are now tweaking the vaccine for the Mozambique trial. They may try to fortify it by adding in extra antigens 鈥� molecular features on the parasite that the immune system is likely to recognise and attack.
Bojang says the vaccine is the first major one to be tested since failure of the so-called 鈥淧atarroyo鈥� vaccine in trials that finished in 1996. Developed in Bogata, Colombia, the vaccine showed early promise, which fizzled out.
In Tanzania, the vaccine was 30 per cent effective, but it failed in The Gambia and Thailand. 鈥淭here was initial excitement, but in the end, we were disappointed,鈥� says Bojang.
Journal reference: The Lancet (vol 358, p 1927)
