Overall 15,000 children in seven African countries are participating in the trial, which represents the furthest that any malaria vaccine candidate has ever progressed.

The preliminary results, which were announced at a malaria forum hosted by the Bill and Melinda Gates Foundation in Seattle, covered 6,000 of the participating children, all aged between 5 and 17 months.

The developers, GlaxoSmithKline and the PATH Malaria Vaccine Initiative, said it showed roughly a 50% reduction in malaria cases in a 12-month period following vaccination.

Results from a group of infants between 6 and 12 weeks old will be announced late next year.