A doctor gives a polio vaccine to a child at a health clinic in Baghdad last week. The CIA says it banned the use of vaccine programs as cover for spying last year — a practice health officials said had wide repercussions. Ahmad Al-Rubaye/AFP/Getty Images hide caption

itoggle caption Ahmad Al-Rubaye/AFP/Getty Images

False-color transmission electron micrograph of a field of whooping cough bacteria, Bordetella pertussis. A. Barry Dowsett/Science Source hide caption

itoggle caption A. Barry Dowsett/Science Source

There today, here tomorrow: A mother holds her child for a measles vaccination in Manila, Philippines, in January. Travelers are bringing measles from the Philippines to the United States. Noel Celis/AFP/Getty Images hide caption

itoggle caption Noel Celis/AFP/Getty Images

This one's virus-free: Matthew Followill, Nathan Followill and Caleb Followill of Kings of Leon performed in Los Angeles in December. Kevin Winter/Getty Images for Radio.com hide caption

itoggle caption Kevin Winter/Getty Images for Radio.com

A school nurse prepares a vaccine against whooping cough before giving it to students at Mark Twain Middle School in Los Angeles. Kevork Djansezian/Getty Images hide caption

itoggle caption Kevork Djansezian/Getty Images

Princeton University's Nassau Hall. DANIEL HULSHIZER/AP hide caption

itoggle caption DANIEL HULSHIZER/AP

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

itoggle caption ROBYN BECK/AFP/Getty Images

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

itoggle caption Daniel Berehulak/Getty Images

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

itoggle caption Kevork Djansezian/Getty Images

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

itoggle caption LM Otero/AP

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

itoggle caption NIAID/Flickr.com

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. iStockphoto.com hide caption

itoggle caption iStockphoto.com

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

itoggle caption Geoff Caddick/AFP/Getty Images

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

itoggle caption Jeff J. Mitchell/Getty Images