Influenza A virus subtype H1N1

Influenza A virus subtype H1N1, also known as A(H1N1), is a subtype of influenzavirus A and the most common cause of influenza in humans. Some strains of H1N1 are endemic in humans, including the strain(s) responsible for the 1918 flu pandemic which killed 50–100 million people worldwide. Less virulent H1N1 strains still exist in the wild today, causing roughly half of all flu infections in 2006.[1] Other strains of H1N1 are endemic in pigs and in birds.



1.In March and April 2009, an outbreak of H1N1 influenza in Mexico led to hundreds of confirmed cases and a number of deaths.
2. As of April 28, the new strain was suspected to have infected more than 2,500 individuals worldwide, with 152 attributed deaths. The U.S. Centers for Disease Control and Prevention warned that it was possible the outbreak could develop into a pandemic.
3. On April 27, 2009, the World Health Organization raised their alertness level from 3 to 4 (on a scale of 6) worldwide in response to sustained human-to-human transfer of the virus. The situation was raised to level 5 (pandemic imminent) on April 29, 2009 by the World Health Organization.
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Influenza A virus strains are categorized according to two viral proteins, hemagglutinin (H) and neuraminidase (N). All influenza A viruses contain hemagglutinin and neuraminidase, but the structure of these proteins differs from strain to strain due to rapid genetic mutation in the viral genome. Influenza A virus strains are assigned an H number and an N number based on which forms of these two proteins the strain contains.