| Pandemic H1N1/09 virus | |
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| Transmission electron micrograph of the pandemic H1N1/09 influenza virus photographed at the CDC Influenza Laboratory. The viruses are 80–120 nanometres in diameter.[1] | |
Virus classification 
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| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phylum: | Negarnaviricota |
| Class: | Insthoviricetes |
| Order: | Articulavirales |
| Family: | Orthomyxoviridae |
| Genus: | Alphainfluenzavirus |
| Species: | |
| Strain: | Pandemic H1N1/09 virus
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| Influenza (flu) |
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The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.
The H1N1 pandemic of 2009 was the first public health emergency of international concern designated by the World Health Organization. While H1N1/09 was the primary strain of flu seen that year, it was not unusually contagious or lethal.
Most cases were mild, although those who had to be hospitalized were often severely ill. In the fall of 2009, between 15-33% of those hospitalized with H1N1 in the Southern Hemisphere were taken to the ICU. One clinician remarked that the pandemic was "like two diseases" because of the stark difference between mild and severe cases, with few falling in between.
- ^ International Committee on Taxonomy of Viruses. "The Universal Virus Database, version 4: Influenza A". Archived from the original on January 13, 2010.