Michele Pereira, who questions the schedule of mandatory vaccines, sat with her daughters, Evangeline, 6, right, and Genevieve, 2, at a park in Ashland, Ore., earlier this month. Jeff Barnard/AP hide caption

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What's in this vial changes from year to year, but the process of creating the flu vaccine remains pretty constant.

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A Haitian protester in Port-au-Prince last month spray-paints a wall, equating the UN mission in Haiti (abbreviated here as MINISTA) with cholera.

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A mother held her baby as she received an experimental malaria vaccine at the Walter Reed Project Research Center in Kombewa in Western Kenya in Oct. 2009.

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University of Miami pediatrician Judith L. Schaechter gives an HPV vaccination to a 13-year-old girl last week in Miami. Joe Raedle/Getty Images hide caption

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A nurse vaccinates a child against pneumonia at a healthcare center in Managua in January. Nicaragua received pneumococcal vaccines from the GAVI Alliance. ELMER MARTINEZ/AFP/Getty Images hide caption

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Trevor Reese, 13, gets his diphtheria, tetanus and pertussis booster shot from pediatric nurse practitioner Jenny Lu in Tustin, Calif., in August. Jae C. Hong/AP hide caption

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