Colombian biochemist Manuel Patarroyo, who nearly a decade ago made what he claims is "the first vaccine to protect against malaria", has no doubts: the vaccine works. He has found the vaccine to be effective in monkeys and has tested it with apparent success in clinical trials involving thousands of people in Latin America. But many scientists, mainly in Europe and the United States, remain sceptical, citing difficulties in reproducing Patarroyo's findings in monkeys and faulting the trials for their poor design.