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Malaria vaccine shows promise

November 15, 2005 By Simon Frantz This article courtesy of Nature News.

Children in trial are protected for at least 18 months.

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Scientists are hailing the findings from a malaria vaccine trial as a huge advance in the fight against the disease. The vaccine, called RTS,S, reduced the incidence of severe malaria by around half in children in Mozambique.

"This is an amazing moment in the history of malaria vaccine development," said Melinda Moree, director of the Malaria Vaccine Initiative, when the results were announced at the fourth Multilateral Initiative on Malaria Pan-African Conference in Yaoundé, Cameroon. The results are published online in The Lancet1.

Many hope that RTS,S is the answer to protecting against a disease that kills more children under the age of five than any other infectious agent. But Moree and others in the field stress that the most important message is simply that it is possible to make a successful vaccine. Even if RTS,S does not work out in further trials, they note, these positive results mean it will be worth pursuing the option of vaccination.

"The findings confirm the potential of malaria vaccines as credible control tools for public health," says the lead author of the study, Pedro Alonso from Barcelona University in Spain.

Essential tool

An effective vaccine is becoming necessary. The parasite that causes malaria, called Plasmodium falciparum, is becoming more resistant to drugs, and the mosquitoes that carry it are becoming resistant to insecticides.

Even at the start of the decade, few believed that a vaccine could conquer the malaria parasite. Current vaccines only target bacteria and viruses. And the parasite is a cunning foe: it goes through several guises on its travels between mosquitoes and humans, each time changing the proteins found on its cell surface.

Vaccines work by binding to these proteins and informing the immune system that there is an intruder present. Making a vaccine that targets a single protein is therefore unlikely to provide adequate protection.

Undeterred, several researchers have tried to develop vaccines that could conquer the seemingly invincible. There are about 75 vaccines or vaccine concepts under development, but all eyes are on RTS,S, because it is in the most advanced stage.

The vaccine is being developed by GlaxoSmithKline Biologicals, based in Rixensart, Belgium, with the help of the Stockholm-based Malaria Vaccine Initiative.

Early results with RTS,S were positive, but hardly conclusive. Adults in Gambia were protected by the vaccine, but there were suggestions that this effect would be short-lived (see ' Save the children').

Results from an interim trial in more than 2,000 children aged 1-4 years in Mozambique showed that RTS,S reduced incidence of severe malaria by around 58%, six months after receiving the vaccine2.

The latest study follows these same children for an additional 12 months, and shows that the vaccine's effect does not appear to wane. The team is now working on modifying the vaccine or mixing it with compounds that could boost the protection even more.

More to come

Despite the positive findings in this 18-month study, there is still much work to be done, including further trials, before this vaccine can be given to the people who need it.

Efforts to combat malaria received a boost last month from the Seattle-based Bill and Melinda Gates Foundation, which announced an injection of US$107.6 million towards launching more trials of RTS,S. If all goes well, the funds would stretch towards taking a vaccine through licensing and introduction to African immunization programmes.

"We can talk about a potential vaccine in five or six years time," says Moree. "But we can't promise a vaccine then."

References

  1. Alonso P. L., et al. Lancet, Published online doi:10.1016/S0140-6736(05)67669-6 (2005).
  2. Alonso P. L., et al. Lancet, 364. 1411 - 1420 (2004).

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