In the spring of 2009, a novel influenza A (H1N1) virus emerged. It was detected first in the United States and spread quickly across the United States and the world. 

This new H1N1 virus contained a unique combination of influenza genes not previously identified in animals or people. ...

From April 12, 2009 to April 10, 2010, CDC estimated there were 60.8 million cases (range: 43.3-89.3 million), 274,304 hospitalizations (range: 195,086-402,719), and 12,469 deaths (range: 8868-18,306) in the United States due to the (H1N1)pdm09 virus.
Additionally, CDC estimated that 151,700-5...

Though the 2009 flu pandemic primarily affected children and young and middle-aged adults, the impact of the (H1N1)pdm09 virus on the global population during the first year was less severe than that of previous pandemics.
The (H1N1)pdm09 virus was very different from H1N1 viruses that were...