Hurricane Sandy's tear across the Caribbean left at least 54 dead in Haiti, where many people still live in tents because of damage from the 2010 earthquake. Thony Belizaire/AFP/Getty Images hide caption

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Dr. Esther Dalizu holds a pack of Coartem Malaria drugs in a pharmacy in Nairobi, Kenya, last year. Sayyid Azim/AP hide caption

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Health employees protest outside the Health Ministry in Athens against pay and budget cuts. Fewer resources for malaria treatment and mosquito control may be contributing to malaria's comeback in Greece. Aris Messinis/AFP/Getty Images hide caption

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Health workers transport the polio vaccine by donkey in southeastern Pakistan. Asad Zaidi/Courtesy of UNICEF Pakistan. hide caption

itoggle caption Asad Zaidi/Courtesy of UNICEF Pakistan.

The iPhone app Electronic Smoke simulates smoking by detecting sound waves. When you breathe into the microphone, the virtual cigarette burns. Screenshot from Electronic Smoke. hide caption

itoggle caption Screenshot from Electronic Smoke.

An Indian child receives the oral polio vaccine. Twice a year, an army of 2 million volunteers fans out across India to administer the vaccine. India has not reported a single case of polio in more than a year-and-a-half. Julie McCarthy/NPR hide caption

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Under the microscope, Mycobacterium tuberculosis bacteria. The germs that cause TB have become resistant to many drugs. Janice Haney Carr/CDC hide caption

itoggle caption Janice Haney Carr/CDC

Children in a Lahore slum after heavy rains. The slum has a large population of Pashtuns who came from Pakistan's lawless tribal regions; many carry the polio virus with them. Jackie Northam/NPR hide caption

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Sahya Idriss, a service provider at the health clinic in Minjibir, carries a vial of the polio vaccine. David Gilkey/NPR hide caption

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During the peak of the polio epidemic in the U.S., some hospital wards even had large, room-like iron lungs where multiple children lived. Courtesy of Boston Children's Hospital Archive hide caption

itoggle caption Courtesy of Boston Children's Hospital Archive

More than 90 percent of Kenyans use mobile phones, giving scientists a powerful tool to track how diseases spread. Simon Maina/AFP/Getty Images hide caption

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When a case of the potentially lethal H5N1 bird flu was found in British poultry in 2007, Dutch farmers were told to keep their poultry away from wild birds by closing off outdoor areas with wire mesh. Ed Oudenaarden/AFP/Getty Images hide caption

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Different types of coronaviruses can cause a simple cold or a deadly respiratory illness, such as SARS. BSIP/UIG via Getty Images hide caption

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