2009 swine flu pandemic in japan 2009 swine flu pandemic in japan the 2009 japan flu pandemic was an outbreak of the h1n1 and the influenza a viruses across japan. the world health organization raised the pandemic alert for influenza to level 4 in april 2009 following a worldwide outbreak of the h1n1 influenza strain. the first japanese infections of h1n1 and influenza a were both recorded early in may 2009. in august 2009, the government estimated that the virus strains had infected about 760,000 people. at the height of the pandemic in october 2009, it was estimated that 20% of the japanese population had been infected and that there were on average more than 20 infected people in each japanese medical facility. the ministry of health, labor and welfare reported 198 deaths as of march 30, 2010. japan put several measures in place to attempt to control the spread of infection including quarantining air travellers entering japan who were suspected of having the virus and closing schools in areas of japan with high numbers of infection. the pandemic ended in august 2010 when the world health organization announced that worldwide influenza infection number were back to the seasonal average before the outbreak occurred.