Influenza pandemic

An influenza pandemic (or global epidemic) occurs when a new influenza virus

emerges and spreads around the world, and most people do not have immunity.

This definition is controversial. Central to this debate has been the question of whether

H1N1 influenza should have been labelled a “pandemic” at all. The Council of Europe

voiced serious concerns that the declaration of a pandemic became possible only after

WHO changed its definition of pandemic influenza. The formal definitions of pandemics

by WHO can be seen in the “WHO’s pandemic influenza preparedness guidelines”,

first developed in 1999 and revised in 2005 and 2009. However, none of these

documents contains what might reasonably be considered a formal definition of

pandemic influenza, a fact that may explain why WHO has refrained from offering a

quotable definition despite its repeated assurances that “the definition” was never

changed. The startling and inevitable conclusion is that despite ten years of issuing

guidelines for pandemic preparedness, WHO has never formulated a formal definition

of pandemic influenza. WHO’s defence of its decision to declare H1N1 influenza a

pandemic because it met “hard to bend”, “clearly defined virological and

epidemiological criteria” overlooks the fact that these criteria changed over time. As

Gross noted, under WHO’s previous (2005) guidelines the 2009 H1N1 virus would not

have been classified as a pandemic influenza virus simply because it was not a new

subtype. The 2009 plan, by contrast, only required a novel “reassortant” virus. (1)

(1) WHO: Bulletin of the World Health Organization. The elusive definition of pandemic

influenza.