The world's most advanced malaria candidate vaccine offers young children partial protection that wanes with time, but could shield millions against the deadly parasite, its developers said Friday.

Researchers published the final results of a years-long trial with the drug RTS,S in The Lancet medical journal.

"We finally have in our sights a candidate vaccine that could have a real impact on this terrible disease that affects many children during their first years of life," principal investigator Kwaku Asante said in a statement.

"The large number of children affected by malaria, sometimes several times per year, means that this vaccine candidate, if deployed correctly, has the potential to prevent millions of cases of malaria," Asante added.

The trial saw nearly 15,500 children in seven African countries -- one group aged five to 17 months and the other six to 12 weeks -- given three initial vaccine doses over a period of three months.

Some received a booster shot 18 months later -- the effects of which were reported for the first time on Friday.

The extra dose, it turned out, "restores some of the immunity lost after the first series of injections," according to study co-author Brian Greenwood of the London School of Hygiene and Tropical Medicine.

"Unfortunately, this is not as big an effect as that seen with some other vaccines," like that against measles, he told AFP by email.

In spite of the drug's partial effect, it remains the most clinically-advanced vaccine against malaria, which kills about 1,200 children in sub-Saharan Africa on average per day.

Compared to children not given the vaccine, those in the older age group enjoyed a protection rate of about 50 percent in the first year against clinical or non-life threatening malaria -- dropping to 28 percent after four years, said the study released on the eve of World Malaria Day on Saturday.

The extra dose increased the protection rate at year four to 36 percent.

The comparable figures for the younger group was 18 percent after three years, and 26 percent with the booster.

For severe malaria, those in the older group who received an extra shot enjoyed a protection rate of 32 percent after four years, said Greenwood -- but without a booster the vaccine offered no noticeable defence.

Developed with the backing of drug firm GlaxoSmithKline and non-profit group PATH Malaria Vaccine Initiative, with funding from the Bill & Melinda Gates Foundation, RTS,S is the first candidate malaria vaccine to reach Phase III clinical testing -- the final stage before market approval.

The mosquito-borne disease kills some 600,000 people per year -- more than 75 percent of them children under five, according to the World Health Organization (WHO).

Approached for comment on the study, University of Oxford tropical medicine professor Nick White said the findings were both encouraging and disappointing.

"We at last have a vaccine against malaria that works -- but it doesn't work as well as originally hoped," he said.

And it was not clear if the findings warrant a widespread vaccination campaign.

"It depends on the costs and the benefits," said White. "If there is enough money, yes. If this will draw money away from control measures of proven value (drugs and bed nets) then no."

- Meningitis risk? -

The European Medicines Authority is evaluating whether or not the drug can be licenced for use, and the WHO is preparing policy recommendations for what could be the first licenced vaccine against a parasitic disease.

The trial did not answer the question of how often a booster would be needed, or how many times it would be safe to administer one.

"The results available so far suggest that this might need to be done every year or every two years," Greenwood said.

Some two dozen vaccinated children developed meningitis, but the researchers said this could be coincidental -- an issue that requires further investigation.

They also noted that children who did not receive the booster ran a higher risk of severe malaria towards the end of the study period.

The killer parasite has developed resistance to successive treatments, and insecticide-treated bed nets remain one of the most effective prevention methods.
Source: AFP