A pandemic (from Greek πᾶν pan “all” + δῆμος demos “people”) is an epidemic of infectious disease that is spreading through human populations across a large region; for instance a continent, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic. Further, flu pandemics exclude seasonal flu. Throughout history there have been a number of pandemics, such as smallpox and tuberculosis. More recent pandemics include the HIV pandemic and the 2009 flu pandemic.
According to the World Health Organization (WHO), a pandemic can start when three conditions have been met: 1
– emergence of a disease new to a population;
– agents infect humans, causing serious illness; and
– agents spread easily and sustainably among humans.
A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious.
In a virtual press conference in May 2009 on the influenza pandemic Dr Keiji Fukuda, Assistant Director-General ad Interim for Health Security and Environment, WHO said “An easy way to think about pandemic … is to say: a pandemic is a global outbreak. Then you might ask yourself: “What is a global outbreak”? Global outbreak means that we see both spread of the agent … and then we see disease activities in addition to the spread of the virus.” 2
In planning for a possible influenza pandemic the WHO published a document on pandemic preparedness guidance in1999, revised in 2005 and during the 2009 outbreak, defining phases and appropriate actions for each phase in an aide memoire entitled WHO pandemic phase descriptions and main actions by phase 3. All versions of this document refer to influenza. The phases are defined by the spread of the disease; virulence and mortality are not mentioned.
1.”Avian influenza frequently asked questions” (in en). World Health Organization. December 5, 2005. http://www.who.int/csr/disease/avian_influenza/avian_faqs/en/. Retrieved 2009-02-13. “A pandemic can start when three conditions have been met: a new influenza virus subtype emerges; it infects humans, causing serious illness; and it spreads easily and sustainably among humans.”
2.WHO press conference on 2009 pandemic infuenza
3.WHO pandemic phase descriptions and main actions by phase
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