What Is a Pandemic?

Abstract

The sudden emergence and rapid global spread of a novel H1N1 influenza virus in early 2009 [1] has caused confusion about the meaning of the word “pandemic” and how to recognize pandemics when they occur. Any assumption that the term pandemic had an agreed-upon meaning was quickly undermined by debates and discussions about the term in the popular media and in scientific publications [2–5]. Uses of the term by official health agencies, scientists, and the media often seemed to be at odds. For example, some argued that a level of explosive transmissibility was sufficient to declare a pandemic, whereas others maintained that severity of infection should also be considered [2–5] Commentators questioned whether we could effectively deal with a pandemic when we could not agree on what a pandemic is or whether we were experiencing one. Amid this discussion, a New York Times commentary, published 8 June 2009, struck at the heart of the problem with its challenging headline, “Is This a Pandemic? Define ‘Pandemic’” [5]. Three days later, the World Health Organization (WHO) announced that the pandemic alert for the 2009 H1N1 influenza virus had been raised to its highest level, “phase 6.”