Kimberly Delp gives a flu shot to Carleen Matthews at the Homewood Senior Center in Pittsburgh, Pa., last September. Andrew Rush/AP hide caption

itoggle caption Andrew Rush/AP

More than 400 guns, including these three, were turned in during a Dallas gun buyback program in January. But determining the effectiveness of such programs is difficult due to limits on gun-related research. Tom Pennington/Getty Images hide caption

itoggle caption Tom Pennington/Getty Images

Sonia Despiar, right, a nurse with Gouverneur Healthcare Services, injects Imelda Silva with flu vaccine on Friday, Jan. 11, 2013, in New York. At least 10 elderly people and two children in New York have died from the flu and hospitalizations are climbing as the illness hits every county in the state. Bebeto Matthews/AP hide caption

itoggle caption Bebeto Matthews/AP

Registered nurse Michelle Newbury and physician assistant Scott Fillman see patients Thursday in a tent set up for people with flu symptoms, just outside the emergency entrance at the Lehigh Valley Hospital in Allentown, Pa. Matt Rourke/AP hide caption

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A picture from the photo story "Keg Stand Queens," which explores the gender dynamics of undergraduate binge drinking. Amanda Berg/The Alexia Foundation for NPR hide caption

itoggle caption Amanda Berg/The Alexia Foundation for NPR

An overweight child reads her part during a skit that was in a 2010 program promoting healthy lifestyles sponsored by Children's Hospital near Denver. John Moore/Getty Images hide caption

itoggle caption John Moore/Getty Images

The U.S. Army distributed a monthly pinup calendar to GIs, which encouraged them to protect themselves from malaria-carrying mosquitoes. Cartoon by Frank Mack for the U.S. Army./Courtesy of the Images from the History of Medicine. hide caption

itoggle caption Cartoon by Frank Mack for the U.S. Army./Courtesy of the Images from the History of Medicine.

The Centers for Disease Control and Prevention says the accidental release of chlorine gas at a Tyson Food plant could have been prevented with better communication. April L Brown/AP hide caption

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At a Los Angeles media briefing in 2010, Mariah Bianchi describes how her own case of whooping cough caused the death of her newborn son. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

Hospitals began testing blood for hepatitis in 1992, so anyone who received a blood transfusion before then is at an increased risk for contracting the disease. iStockphoto hide caption

itoggle caption iStockphoto

Each dot represents one case of mumps between late June 2009 and late June 2010. The New England Journal of Medicine hide caption

itoggle caption The New England Journal of Medicine