As I said there is probably no official WHO definition or criteria due to big economic impact of such declaration and it is decided on a case by case basis. ED

As I said there is probably no official WHO definition or criteria due to big economic impact of such declaration and it is decided on a case by case basis. EDIT: I was wrong, here is the chart: https://www.who.int/influenza/resources/documents/pandemic_phase_descriptions_and_actions.pdf https://www.who.int/influenza/resources/documents/pandemic_p...