HPV vaccine prevents cervical cancer and other cancers by fending off the virus that causes them. But it's been a tough sell with doctors and parents. Joe Raedle/Getty Images hide caption

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The varicella zoster virus causes chickenpox in children, then lurks in the body for years and can cause painful shingles later in life. James Cavallini/Science Source hide caption

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A family receives treatment for cholera at a clinic run by Doctors Without Borders in Port-au-Prince, Haiti, in October 2011, a year after the overwhelming outbreak began. Ramon Espinosa/AP hide caption

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Most of the people who got measles in last year's outbreaks hadn't been vaccinated with the MMR vaccine. Photo illustration by Justin Sullivan/Getty Images hide caption

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Parents and teachers who oppose efforts to end the personal belief exemption on vaccinations rally in Los Angeles on April 14. Irfan Khan/LA Times via Getty Images hide caption

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Parents rally against SB 277, a California measure requiring schoolchildren to get vaccinated, outside the Capitol in Sacramento, Calif. Rich Pedroncelli/AP hide caption

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A security fence surrounds the main part of the U.S. Army's Dugway Proving Ground, a testing laboratory in the Utah desert. The Army says it mistakenly shipped live anthrax from Dugway to several labs in the U.S. and Korea. George Frey/Getty Images hide caption

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Worth a little pain? Back in 1990, a school boy got a measles shot in the U.K., and it turns out, he got more than protection against the measles. Photofusion/UIG via Getty Images hide caption

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Australian Prime Minister Tony Abbott looks during a news conference at Parliament House in Canberra, Australia, last month. Abbott announced Sunday that his government would close a loophole to discourage families from refusing childhood vaccinations. Lukas Coch/EPA/Landov hide caption

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