Infants aged 6-12 weeks who received the candidate vaccine RTS,S had one-third fewer episodes of clinical malaria - including one-third fewer severe episodes - than infants who received a control vaccine. In terms of side-effects, reactions to the two vaccines were similar.

The trial was conducted at 11 research centres in seven African countries, including at the KEMRI-Wellcome Trust Research Programme, one of the Wellcome Trust's Major Overseas Programmes. The trial was carried out together with GSK and the PATH Malaria Vaccine Initiative (MVI), with funding from the Bill & Melinda Gates Foundation to MVI.

Despite significant recent progress in the battle against malaria, the disease still kills 655 000 people a year, mainly children under five in sub-Saharan Africa.

RTS,S is designed to trigger the immune system to defend against the malaria parasite Plasmodium falciparum when it first enters the bloodstream or when it infects liver cells. The aim is to prevent the parasite from infecting, maturing and multiplying in the liver, after which it would normally re-enter the bloodstream and infect red blood cells, leading to disease symptoms.

The trial covered infants who received their first RTS,S injection in a series of three at age 6-12 weeks, administered along with standard childhood vaccines, and a second group who received a control vaccine at that age. In 12 months of follow-up after the third injection, the efficacy of RTS,S was 31 per cent against clinical malaria and 37 per cent against severe malaria.

Insecticide-treated bed nets were used by 86 per cent of the trial participants, which demonstrates that the superior protection given by RTS,S was over and above that of this existing malaria control intervention.

A trial of RTS,S in 2011, in children aged 5-17 months, found 56 per cent efficacy against clinical malaria and 47 per cent against severe malaria. Follow-up in this phase III trial will continue and is expected to provide more data to better understand the difference in findings between the age categories.

Sir Andrew Witty, Chief Executive of GSK, said: "While the efficacy seen is lower than last year, we believe these results confirm that RTS,S can help provide African babies and young children with meaningful protection against malaria. They take us another important step forward on the journey towards having a new intervention available against this disease, which is a huge burden on the health and economic growth of Africa.

"We remain convinced that RTS,S has a role to play in tackling malaria and we will continue to work with our partners and other stakeholders to better understand the data and to define how the vaccine could best be used to provide public health benefit to children in malaria-endemic areas in Africa."