A new kind of bed net against malaria is a two-year trial involving more than 15,000 children has shown that it can significantly increase protection against the mosquito-borne disease. This trial in Tanzania showed that a long-lasting insecticidal net treated with a chemical called piperonyl butoxide (PBO LLIN) reduced the prevalence of malaria by 44 percent and 33 percent in the first and second year respectively, compared to a standard net treated with pyrethroid only. The trial is the first clear evidence that nets treated with piperonyl butoxide can significantly improve personal and community protection from malaria compared to standard pyrethroid-only nets in areas where there is high pyrethroid resistance. It also demonstrated that pyrethroid resistance is now a significant problem in some areas and standard LLIN are less effective than before and that the new IRS controlled malaria for an entire year before needing to be re-sprayed. Anticipating the possible failure of current control tools due to resistance, the World Health Organization (WHO) and the London School of Hygiene and Tropical Medicine have been collaborating with the chemical industry for almost 20 years to develop new types of Long Lasting Insecticide Net (LLIN) and new insecticides for IRS. The novel LLIN which incorporates piperonyl butoxide (PBO), is a chemical which blocks the natural defence mechanisms of insects the oxidase enzymes. This chemical synergist stops insects from breaking down the pyrethroid within their bodies, so the insecticide stays toxic to the insect.