In a clinical trial involving more than 2,000 children under the age of five, a potential malaria vaccine was shown to be safe and well tolerated by the children's immune system for up to six months.
The results of the one-year trial that took place in Mozambique appear in this week's issue of The Lancet.
The results have been called a breakthrough in malaria vaccine development. But even if the vaccine were successful in the next stages of testing, it would not be ready until 2010.
By then, experts predict that nearly 3.5 billion people will be living in malaria-endemic areas. Malaria currently kills between one and three million people every year — mostly African children under the age of five.
The scientists investigated the vaccine's effectiveness in 2,022 children between the ages of one and four years. Half the children received three doses of the vaccine and the other half was given control vaccines against meningitis or hepatitis B.
The majority — 58 per cent — of the children were protected from life-threateningly severe disease, whereas 30 per cent were protected from a clinical malaria attack — one that requires hospitalisation.
The researchers also investigated whether the vaccine could prevent new infection. They found that 45 per cent of the children who participated in this part of the trial were protected against a new infection.
The vaccine works by boosting the human immune system so that when a mosquito injects the parasite into the bloodstream, human immune cells and proteins attack and destroy it.
However, making the vaccine work in children with HIV could prove difficult, warn Philippe Van de Perre and Jean-Pierre Dedet in an accompanying commentary in the journal.
They say that since the vaccine relies on strengthening the immune system, its effectiveness is likely to be much lower in HIV-infected children whose immune systems are already weakened.
Other malaria vaccines currently under investigation work by modifying the parasite's path after infection, and by blocking further transmission.
Ultimately, the best malaria vaccine will probably combine different mechanisms, Allan Saul of the Malaria Vaccine Development Unit at the National Institutes of Health told SciDev.Net. He added that a combined vaccine would probably not be a reality for at least another decade.
Since vaccine development is a lengthy process, Saul maintains that measures such as impregnated bed nets and artemisinin-combination treatments are just as crucial in the fight against malaria. In the future, he says, these should be used together with vaccines in an integrated control programme.
In a press conference on 14 October, Jean Stéphenne, president of GlaxoSmithKline Biologicals, which co-sponsored the trial, said the company could not currently estimate what the vaccine would cost: "we expect that the price of the vaccine, if successfully licensed, will be reasonable, and accessible to those who need it most".
Marie-Paule Kieny of the World Health Organisation told SciDev.Net that funding is likely to be a major issue. Pharmaceutical companies have in the past been reluctant to invest hugely in the development of drugs or vaccines that promise little commercial gain.
Thus, much of the funding for malaria vaccine production and distribution is likely to come from organisations such as the Global Alliance for Vaccines and Immunisation (GAVI).
GAVI's Tore Godal told SciDev.Net that the organisation's US$1.3 billion vaccine fund would help finance the distribution of vaccines to the world's poorest countries.
Kieny added that future tests will need to focus on children who are less than one year old, for whom the risk of infection is high and who are most severely affected by the disease.
Although 15 children died during the trial and a few children suffered serious adverse effects, the researchers do not believe this was attributable to the vaccine.
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The Lancet 364, 1411 (2004)
The Lancet 364, 1380 (2004)