Reuters - Tue Jul 26,12:06 PM ET
Strains of the influenza virus are constantly swapping genes among themselves and giving rise to new, dangerous strains at a rate faster than previously believed, U.S. researchers reported on July 25, 2005. File photo shows an Influenza Virus Vaccine vial sitting on the counter of medical center in Great Neck, New York October 22, 2004. (Shannon Stapleton/Reuters)