What Is a Pandemic?
David M. Morens, Gregory K. Folkers, Anthony S. Fauci
The Journal of Infectious Diseases, Volume 200, Issue 7, 1 October 2009, Pages 1018–1021,
https://doi.org/10.1086/644537
Published:
01 October 2009
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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.”
Because it is generally agreed that we are currently in the midst of a global influenza pandemic caused by the novel H1N1 2009 influenza virus, it may now be a good time to ask again: what is a pandemic? Modern definitions include “extensively epidemic” [6], “epidemic … over a very wide area and usually affecting a large proportion of the population” [7, p. 94], and “distributed or occurring widely throughout a region, country, continent or globally” [8], among others. Although they convey the intuitive idea that a pandemic is a very large epidemic, such definitions still seem vague. Although there seems to be little disagreement that a pandemic is a large epidemic, the question arises whether pandemics must be new, explosive, or severe. Must they be infectious at all? And what if they rapidly spread globally without causing high attack rates? In short, how do we know a pandemic when we see one?
In the 17th and 18th centuries, the terms epidemic and pandemic were used vaguely and often interchangeably in various social and medical contexts. The first known use of the word pandemic, in 1666, referred to “a Pandemick, or Endemick, or rather a Vernacular Disease (a disease alwayes reigning in a Countrey)” [9, p. 3]. Two centuries later, in 1828, epidemiologist and lexicographer Noah Webster’s first edition of Webster’s Dictionary listed epidemic and pandemic as synonymous terms [10]. Webster, who had lived through the influenza pandemic of 1789–1790, which was the only major American influenza event of his adult lifetime, refers in his dictionary only to epidemic influenza and not to pandemic influenza [10]. Thus, by the early 19th century, the term epidemic, when used as a noun, had become the accepted term for what we would call today both an epidemic and a pandemic, with the term pandemic falling into increasing disuse
However, as societies were evolving, so too were disease patterns and scientific understanding of how diseases spread. The industrial revolution brought millions of people into urban centers, while clipper ships and steam locomotives dispersed ever-increasing numbers of individuals widely, and even globally. The 1831–1832 cholera pandemic represented the first time that the global spread of an infectious disease was plotted extensively in the popular press, day by day, for more than a year as it progressed inexorably from Asia toward Europe via travel and trade routes. Discovery of the microbial causes of diseases led to vaccines and antisera against them and to widely distributed diagnostic tests to study and monitor diseases at their sources. Under the umbrella of epidemics, the idea of a pandemic thus began to take shape before any specific meaning of the languishing term had become associated with it. When the 1889 influenza pandemic appeared, the concept of a pandemic already existed. The previously vague, imprecise, and infrequently used term was for some reason—perhaps because of influenza’s remarkable explosiveness and the precise tracking of its rapid global spread in 1889 [11]—rescued from near-obscurity and attached to the remarkable global emergence of influenza. Soon thereafter, the term pandemic entered into general use; by 1918, it had become virtually a household word
The 1889 and 1918 influenza pandemics may have temporarily codified the meaning of the word pandemic, but it soon drifted into looseness and imprecision as it began to be used popularly to denote large-scale occurrences of noninfluenza infections and chronic and lifestyle-associated diseases; it thereby returned to a status similar to its former one, denoting almost anything that increased in and appeared to spread within or among groups of people, such as smoking, traffic accidents, factory closings, and even fear [12]. Moreover, with better modern control of such major pandemic diseases as cholera and plague, the term pandemic became closely associated with historical, rather than contemporary, events. In the past 2 decades, many modern medical texts have not even defined the term. Even authoritative texts about pandemics do not list it in their indexes, including such resources as comprehensive histories of medicine [13, 14], classic epidemiology textbooks [15, 16], the Institute of Medicine’s influential 1992 report on emerging infections [17], and acclaimed works about pandemics [18–20]
