Patarroyo's vaccine will allow the human immune system to identify and kill the malaria parasite in the blood stream. This will cut out a vital stage in the parasite's life-cycle which allows it to multiply. If enough people in an area are vaccinated, it could mean wiping out the disease entirely.

Most malaria research has concentrated on killing the parasite as it enters the blood stream. Patarroyo's vaccine is designed to block the parasite at it its later ``merozoite'' form, when it emerges from initial incubation in the liver. The vaccine stimulates the antibodies, which prevent the parasite infecting the red blood cells or assuming their male and female form, in whichthey stay in the blood stream, until a second mosquito bite transfers them back into the body of the mosquito to complete their breeding cycle.A problem that scientists working on the vaccine have faced is that the malaria parasite mutates to avoid being destroyed. Patarroyo has taken a novel approach, inventing a chemical vaccine rather than a biological one. He believes that his vaccine, by using an inert chemical process, prevents the danger of mutation by the parasite. He is already using the same methods to develop a vaccine for the milder, but more common vivax type of malaria, which kills some 100,000 people each year.

Patarroyo first produced a chemical vaccine with partial success in the late 1980s. However, only between 30-50 percent of those vaccinated with that early version developed sufficient antibodies to fight the malaria parasite. He donated the patent of the first version to the WHO.

Brian Greenwood from the School of Tropical Hygiene and Medicine in London was involved with the trialsof the first version of Dr Patarroyo's vaccine in Africa. He told The Guardian: ``There is no reason why, when he refined his methods, the new vaccine would not work. I believe he could succeed. I hope he has.''

Patarroyo's ``30 percent vaccine'' was attacked in the cut-throat world of scientific research, where pharmaceutical companies are major players. He is said to be wary of the international scientific community and is awaiting the review of his trials on the malaria-prone aotus monkey, before beginning human trials.

Greenwood said: ``There is some prejudice because he is from a developing country, but this is so important, I think most people keep an open mind.'' Patarroyo's research has been funded, among others, by the Colombian government and the Rockerfeller Foundation. His work is audited by the WHO and his findings are currently being verified by a peer review. Howard Engers, from the WHO's vaccination programme said: ``I am very impressed by his work and when I last visited him 18 monthsago, his results with monkeys were already very impressive.''

Patarroyo said: ``Since I was eight, I have dreamed of making vaccines, particularly one for malaria. I am not interested in making money - in Colombia, being rich makes you a target anyway. I am prepared to make the vaccine and sell it at cost. The drug companies will not like that and I will face opposition, but think what a difference it will make to the world.''