A malaria vaccine has been found to protect children in Africa from serious disease for at least 18 months.
Malaria kills huge numbers in Africa
Researchers working in Mozambique found the jab cut the risk of clinical malaria by 35% and nearly halved the risk of serious malaria.
The vaccine was already known to offer six months' protection - but experts argued that vaccinating children twice a year was not practical in Africa.
Details were presented to a pan-African malaria conference in Cameroon.
Malaria kills over a million people world-wide each year, and one African child every 30 seconds.
Most experts believe that there is no immediate prospect of a vaccine that could wipe out malaria, or even provide lifelong immunity.
But a vaccine that would turn the disease into a mostly mild infection would make a huge dent in the effort to control malaria.
The latest candidate - GlaxoSmithKline's RTS, S/AS02A - was given to 1,442 children in Mozambique in 2003.
The initial six month follow-up showed that the vaccine reduced the risk of clinical malaria by 30%, and the risk of serious disease by 58%.
The latest follow-up, details of which were published online by The Lancet, found that the protection offered by the jab did not wane after a further 12 months.
Dr Joe Cohen, the vice president of research and development for vaccines for emerging diseases at GlaxoSmithKline, has been working on the prototype for 19 years.
He said further work was already planned on more extensive trials.
"They will involve many thousands of children, probably somewhere between 10,000 and 15,000 children, and it will take another two to two-and-a-half years.
"By 2010 we do hope that we will be able to submit a registration file to the appropriate regulatory authorities."
GlaxoSmithKline has been working with the University of Barcelona, the Ministry of Health in Mozambique and the Malaria Vaccine Initiative to develop the jab since 2001.
Melinda Moree, of the Malaria Vaccine Initiative, said: "We are very excited because there is a malaria vaccine that protects children from malaria and it actually lasts long enough to make it a real public health intervention that can have an impact on malaria in Africa."