World Health Organization (WHO) officials characterize the 2009 H1N1 flu as the fastest spreading pandemic on record.

In March 2009, a novel virus ultimately designated 2009 H1N1 influenza virus (alternately, Type A/H1N1) resulted in cases of influenza (flu) in Mexico and the United States. The novel virus was definitively detected as early as 15 April 2009 by both U.S. and Canadian researchers. Emanating initially from Mexico, the virus quickly spread around the world, and the relative ease of human-to-human transmission of the virus quickly raised fears of a global pandemic. The first official death in the United States was reported on 29 April 2009; the victim was a twenty-three-month-old toddler (reportedly from Mexico City) who was transported from Brownsville, Texas, on the U.S.-Mexican border, to Houston for treatment. On 11 June 2009, WHO declared that the 2009 H1N1 influenza was officially a global pandemic.

Experts usually define a viral pandemic as ... View Full Overview