The new virus should have developed the ability for easy and sustained human-to-human spread. H5N1 virus was unable to cause a pandemic due to its ineffective human to human transmission. In March 2009, a novel strain of H1N1 infl uenza virus evolved from a reassortant between triple re-assortant swine infl uenza viruses in North American pigs and infl uenza A virus circulating in Eurasian pigs [16, 17] . This combination had not been seen previously. By the end of April 2009, WHO declared the emergence of human cases of H1N1 swine infl uenza virus. On 11 June 2009, the WHO raised the pandemic alert from phase 5 to phase 6 and announced that the world was at the beginning of an infl uenza pandemic [18] . 