 Scientists have spent decades trying to produce a vaccine against malaria that's not only effective but affordable. The disease, which is spread by mosquitoes, kills more than 600,000 people a year, many of them in low-income nations. Today, the first doses of the cheapest vaccine to date have been rolled out in Cote d'Ivoire, costing under $4 a jab. The vaccine is the result of decades of research and testing at the University of Oxford in England.