Public school student Julio Valenzuela, 11, grimaces as he gets a vaccination before the start of the school in Lynnwood, Calif., on Aug. 27. Vaccines are required for school attendance. ROBYN BECK/AFP/Getty Images hide caption

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Avez, 2, is held by his mother, as he receives the polio vaccine in the Khyber Tribal Region in northwest Pakistan. Daniel Berehulak/Getty Images hide caption

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A student gets vaccinated against pertussis at a Los Angeles middle school in 2012. The state required that students be immunized to halt an epidemic of whooping cough. Kevork Djansezian/Getty Images hide caption

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The Eagle Mountain Church in Newark, Texas, was linked to at least 21 cases of measles this year, mostly in children. LM Otero/AP hide caption

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A red blood cell infected with malaria parasites (blue) sits next to normal cells (red). NIAID/ hide caption

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Ads often tout dietary supplements and vitamins as "natural" remedies. But studies show megadoses of some vitamins can actually boost the risk of heart disease and cancer, warns Dr. Paul Offit. hide caption

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Luke Tanner, 7, gets vaccinated for measles at a clinic near Swansea, Wales, in April. Wales is at the center of a measles outbreak that has been linked to one death. Geoff Caddick/AFP/Getty Images hide caption

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A new study from the Centers for Disease Control and Prevention finds no link between the number of vaccinations a young child receives and the risk of developing autism spectrum disorders. Jeff J. Mitchell/Getty Images hide caption

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A simple switch of ingredients made a big difference in how mice responded to experimental cancer vaccines. Andrei Tchernov/ hide caption

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Nurse Christel Petersen inoculates a child in the South African Tuberculosis Vaccine Initiative study in 2011. Rodger Bosch/AFP/Getty Images hide caption

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The fall armyworm, a corn pest, is now also a vaccine factory. Wikimedia Commons hide caption

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