Why was the 2009-2010 flu season considered a pandemic?

Answers from James M. Steckelberg, M.D.

The World Health Organization declared the 2009-2010 flu season a pandemic because the novel H1N1 flu (swine flu) had occurred in multiple countries around the world and human infection was widespread. The classification does not reflect the severity of individual infections.

Flu pandemics typically occur when a virus mutates into something very different from what people have been exposed to in the past. The first H1N1 pandemic occurred in 1918 and it killed millions of people. Luckily, the 2009 pandemic was much milder.

Dec. 04, 2010 See more Expert Answers