In this illustration, new viruses emerge from an infected human throat cell. When you get the flu, viruses turn your cells into tiny virus factories that help spread the disease. Courtesy XVIVO/Zirus hide caption

itoggle caption Courtesy XVIVO/Zirus

Michelle Obama jump-ropes Wednesday on the South Lawn of the White House during an event promoting exercise and healthy eating for children. Win McNamee/Getty Images hide caption

itoggle caption Win McNamee/Getty Images

The Centers for Disease Control and Prevention will decide on Wednesday whether to recommend that boys get vaccinated against the human papilloma virus (HPV). iStockphoto.com hide caption

itoggle caption iStockphoto.com