At the end of March/beginning of April 2009, a new type A influenza virus, subtype H1N1 (A/HlNlv), appeared on the world epidemiological scene. This subtype emerged from the re-assortment of two viruses that had long been present in swine in Americas and Eurasia respectively 1. The first human cases of illness were reported in Mexico and the United States, and within a few weeks the virus had spread worldwide with unprecedented speed through direct person-to-person transmission. On account of this rapid evolution, attention regarding preparation and the response to the influenza pandemic was raised by the World Health Organization (WHO) to the maximum level of alert, level 6 (on 11~(th) June 2009), corresponding to an increased and prolonged transmission of the virus in the populations of numerous countries in the world 2.
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