Nurse Susan Peel gives a whooping cough vaccination to a student at Inderkum High School in Sacramento, Calif., in 2011. Now it seems likely such shots will become routine for senior citizens, too. Rich Pedroncelli/AP hide caption

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Even in the remote Faroe Islands, some children have high levels of perfluorinated compounds in their blood. The chemicals may interfere with the immune system. Stig Nygaard/Flickr hide caption

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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.

Karel Prinsloo/AP hide caption

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