Even if suitable steps are taken towards the generation of ‘safe sporozoites’, it is not clear that the children in endemic areas will benefit. The load of parasites to which children are exposed to in endemic areas is already quite large (inoculation rate of >100 per year). Fetal sensitization also occurs for malaria, and children are found to carry detectable loads of parasite87,88, indicating that the exposure to low levels of parasites does not necessarily protect. For most vaccines, Phase I clinical trials are conducted with malaria naïve adults, and such data may not have much relevance for children living in malaria endemic areas. Indeed, immunity to malaria seems to be related to age in an absolute manner. A study of migrant population that had moved from malaria nonendemic to malaria endemic region in Irian Jaya showed that the immunity was acquired faster by adults than children. Subsequently, it has also been shown that this immunity increased during puberty and was predicted by levels of the pubertal steroid dehydroepiandrosterone sulfate. Thus, even the whole sporozoite or the erythrocytic vaccines are likely to be effective only on naïve adults