New research finds a close connection between the flu that devastated the horse population in North America in the 1870s and the avian flu of that period. Hulton Archive/Getty Images hide caption

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The fall armyworm, a corn pest, is now also a vaccine factory. Wikimedia Commons hide caption

itoggle caption Wikimedia Commons

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

itoggle caption Matt Rourke/AP

Four-year-old Gabriella Diaz gets a flu shot at the Whittier Street Health Center in Boston, Mass., on Wednesday, the same day the city declared a public health emergency. Charles Krupa/ASSOCIATED PRESS hide caption

itoggle caption Charles Krupa/ASSOCIATED PRESS

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

itoggle caption Barbara L. Salisbury/The Washington Times/Landov

Chickens are under quarantine in Tepatitlan, Jalisco State, Mexico. The Mexican government declared a national animal health emergency July 2 in the face of an aggressive bird flu epidemic that has infected nearly 1.7 million poultry. Hector Guerrero/AFP/Getty Images hide caption

itoggle caption Hector Guerrero/AFP/Getty Images