A silicone gel implant (left) and a saline gel implant. The FDA agreed to let implants return to the market in 2006, but stipulated that manufacturers track long-term side effects. Spencer Platt/Getty Images hide caption

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A lab technician prepares blood samples from volunteers for viral genotyping at a government-run health center in Bagamoyo, Tanzania, in 2009. Tanzania is currently hosting the final stages of a human trial of a pioneering vaccine against malaria. The vaccine is one of many medical innovations to emerge from Walter Reed over the decades. Tony Karumba/AFP/Getty Images hide caption

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Two women check their cellphones as they hawk their wares on a bridge over the Artibonite River, whose waters are believed to be the source of Haiti's 2010 cholera outbreak. Nicholas Kamm/AFP/Getty Images hide caption

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