Malaria vaccine shows promise
Largest childhood trial of jab raises prospect of routine inoculation.
For the first time, a vaccine in a clinical trial has convincingly shielded children in Africa from contracting malaria.
Researchers hope the results will pave the way for routine jabs in countries stricken by the mosquito-borne disease, which kills an estimated 1 million people every year.
"It's a really great thing to get to this stage," says Melinda Moree, director of the non-profit organization Malaria Vaccine Initiative, based in Rockville, Maryland, which partly funded the clinical trial.
Over 2,000 children in Mozambique, aged between one and four years, were injected with either the vaccine or a placebo. The team reports in The Lancet that those who received the jab were 30% less likely to show fever or early signs of the disease after six months, and nearly 60% less likely to show symptoms of more severe disease1.
Long time coming
Researchers have been seeking a malaria vaccine for decades. But the task is a tough one, because the parasite that causes the disease, Plasmodium falciparum, takes on several different forms as it invades the blood, the liver and then red blood cells. This means that a vaccine that prompts immunity against one form of the parasite is unlikely to protect against other forms.
The malaria vaccine from the most recent trial, called RTS,S/ASO2A, contains an artificial version of a protein that forms part of the parasite's coat after it has first been fired into the blood by a mosquito and when it starts multiplying in the liver. This artificial protein is thought to trigger the immune system into attacking the parasite, to blunt the infection.
In an earlier trial, researchers found that RTS,S/ASO2A protected adults in Africa from the disease, but only for a few weeks2. This is the first trial to show definitively that it protects children, who suffer the vast majority of deaths from the disease, and that it protects them for a longer time.
To improve the vaccine's ability to stave off infection, Hill says that it will be important to combine it with trial vaccines targeted against later stages of the parasite's life cycle. Several dozen other vaccines are being developed, but none is as far along in trials as RTS,S/ASO2A.
Still, Stephen Hoffman of malaria vaccine biotech company Sanaria in Rockville, Maryland, questions where the money will come from to develop the vaccine for the developing world, where pharmaceutical companies will reap little profit. "It's a great shot in the arm for the field, but it's not the end by any stretch of the imagination," he says.
- Alonso P. L., et al. Lancet, 364. 1411 - 1420 (2004).
- Bojang K. A., et al. Lancet, 358. 1927 - 1934 (2001).