A blood test developed by Harvard researchers checks for evidence of past infection with more than a thousand strains of virus, from about 200 virus families. The swine flu virus shown here, A/CA/4/09, rarely infects humans. C. S. Goldsmith/CDC hide caption

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How Many Viruses Have Infected You?

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Which flu vaccine should you get? That may depend on your age and your general health. Joe Raedle/Getty Images hide caption

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Flu Season Brings Stronger Vaccines And Revised Advice

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Google's Flu Tracker Suffers From Sniffles

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Influenza covers it's shell with two types of accessories: the H spike, blue, and the N spike, red. Here the flu particle is sliced open to show its genetic material. Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases hide caption

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

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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

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When flu viruses (in red) accumulate an escape protein too quickly, they exit the cell nucleus (in blue) before they've made enough viral copies to spread the infection. Benjamin tenOever hide caption

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People line up at a Duane Reade pharmacy in New York behind a sign announcing the recent flu outbreak. Andrew Kelly/Reuters/Landov hide caption

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Bad Flu Season Overshadows Other Winter Miseries

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Dr. Tom Nary is the director of health services at Boston College. Tovia Smith/NPR hide caption

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Colleges Try To Curtail Flu Risk For Students

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Physician assistants Scott Fillman (left) and Andrew Hunadi get ready to see patients with flu symptoms, in a tent erected just outside the emergency entrance at the Lehigh Valley Hospital in Allentown, Pa. Matt Rourke/AP hide caption

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Flu Wave Stresses Out Hospitals

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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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Reaching for relief: A customer at a pharmacy in New York City was grabbing some medicine on Thursday. Andrew Kelly /Reuters /Landov hide caption

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Shea Catlin, a nurse practitioner, doses out flu vaccine to give a shot at a CVS Minute Clinic in Arlington, Va., on Jan. 3. Barbara L. Salisbury/The Washington Times/Landov hide caption

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Can You Get A Flu Shot And Still Get The Flu?

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An health official wearing protective gear culls a bird at a poultry farm after a naturally occurring bird flu virus was detected near Agartala, India, in January. Sushanta Das/AP hide caption

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Expert Panel To Give Controversial Bird Flu Research A Second Look

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Ramon Maldonado-Cardenas grimaces as he gets a flu shot from pharmacy student Khoa Truong during a health fair in Sacramento, Calif., last October. Rich Pedroncelli/AP hide caption

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H5N1 avian flu viruses (seen in gold) grow inside canine kidney cells (seen in green). Cynthia Goldsmith/CDC hide caption

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H5N1 avian flu viruses (seen in gold) grow inside canine kidney cells (seen in green). Cynthia Goldsmith/CDC hide caption

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U.S. Says Details Of Flu Experiments Should Stay Secret

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