According to a recent announcement by the WHO, the H1N1 influenza virus is now the dominant influenza strain in most parts of the world and in the northern hemisphere to prepare for a second wave of pandemic spread.

To date, there are no signs that the virus has mutated to a more virulent or lethal form.

The overwhelming majority of patients continue to experience mild illness. Although the virus can cause very severe and fatal illness, also in young and healthy people, the number of such cases remains small.

How is H1N1 different from seasonlal influenza?

To date, most severe cases and deaths have occurred in adults under the age of 50 years, with deaths in the elderly comparatively rare. This age distribution is in stark contrast with seasonal influenza, where around 90% of severe and fatal cases occur in people 65 years of age or older.

Perhaps most significantly, a very severe form of disease is also observed in young and otherwise healthy people, which is rarely seen during seasonal influenza infections. In these patients, the virus directly infects the lung, causing severe respiratory failure. Saving these lives depends on highly specialized and demanding care in intensive care units, usually with long and costly stays.

The WHO provides information on how to best prepare for and respond to the pandemic: http://www.who.int/csr/disease/swineflu/en/

See also the GreenFacts summary on Global Public Health Threats