Overview: Pandemics

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Author: Dr. Ronald St. John

Throughout history there have been outbreaks of infectious diseases. The well-known plague epidemic (Black Death) was a devastating global epidemic of bubonic plague that struck Europe and Asia in the mid-1300s, wiping out an estimated one-third of the population. Disease outbreaks, when large in scope, have been referred to as epidemics. More recently, epidemics that have involved or might involve the global population have been labelled as pandemics.

When does an epidemic become a pandemic? There is no single accepted definition of the term pandemic (ref: Journal of Infectious Diseases, Vol. 200:7, 1 October 2009). Some considerations for labelling an outbreak as a pandemic include outbreaks of diseases:

  • that extend over large geographic areas, e.g., influenza, HIV/AIDS
  • that have high attack rates and explosiveness, e.g., common-source acquisition and highly contagious diseases with short incubation periods
  • that affect populations with minimal population immunity
  • that involve a new or novel version of an infectious agent – the term pandemic has been used most commonly to describe diseases that are new, or at least associated with novel variants of existing organisms, e.g., influenza.
  • that are highly contagious. Many, if not most, infectious diseases considered to be pandemic by public health officials are contagious from person to person
  • that have severe health consequences. The term pandemic has been applied to severe or fatal diseases

For purposes of this paper, a pandemic is an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.(1)

Why are pandemics inevitable?

The worst kinds of pathogens — ones with the highest mortality rates and limited countermeasures — are increasing due to population increases, population density, more global travel, and changing migratory and environmental patterns that result in encroachment upon animal and other populations.

  • Population density – The world’s population is around 7,500,000,000 people.(2) Excluding Antarctica and considering only the Earth’s land area, population density is 55 people per km2 (over 142 per sq. mile). Around 55 percent of the world’s population is thought to be living in an urban area or city, with that figure set to rise to 68 percent over the coming decades, according to the “Population Division” report.(3)
  • Rapid Population Movement — The International Air Transport Association (IATA) expects 7.2 billion passengers to travel in 2035, a near doubling of the 3.8 billion air travelers in 2016.(4)
  • War/Insurgency – Syria and polio; Yemen and cholera
  • Emergence of New/novel pathogen – mutation of known pathogen or exposure to novel pathogen, e.g., by human encroachment on deforested land
  • Cultural resistance – risks of transmission and poor disease outcomes may be amplified by unfavourable behaviours, with reluctance to adopt prevention and risk mitigation strategies.
  • Fear and resistance to intrusion of outsiders
  • Government cover-up; concern for economic impacts
  • The intensity and spread of infectious disease outbreaks are highly influenced by the social determinants of health. Poor housing, poverty, and lack of access to health care decrease resiliency to cope with communicable diseases, leading to more transmission and/or more morbidity and mortality.


Until some of the basic conditions that favour the expansion of an epidemic to a pandemic are addressed, future pandemics are inevitable. Early detection and coupled with efficient and effective management of a rapid response to contain a disease outbreak at the local level will hopefully minimize the health impact on the global population.

However, much more attention is warranted. Many pandemics are zoonoses — diseases that can be transmitted to humans from animals. Influenza, tuberculosis, bubonic plague, and AIDS (Acquired Immune Deficiency Syndrome) are examples. In fact, today the most promising work on the spread of infectious diseases is being carried out by physicians specializing in epidemiology, veterinary and environmental medicine, working jointly as an inter-disciplinary approach called “One Health.” As wildlife habitats are destroyed to make room for human settlements, and as local climates change with global warming, there are new opportunities for zoonoses to spread. One Health researcher seek to identify these situations quickly, as they emerge worldwide.

In previous times, some virulent diseases had a self-limiting effect; infected people might die quickly -—before they had time to spread their pathogens widely. However, the ease of air travel now makes it possible for infected persons to spread a disease to other continents even before showing symptoms themselves. Thus, the risk of pandemics remains high, despite the spread of advanced medical technology.

Estimates about the probability of a virulent global pandemic are only guesses, but even the most ominous predictions cannot be dismissed. Bill Gates, who is allocating large funds to solving global health problems, sees pandemics as the greatest immediate threat to humanity. He warns that an influenza epidemic alone may kill over 30 million people in six months.(5) Another researcher, David Mannheim, predicts an even more dire possibility. Noting that it is more difficult than ever before to contain an epidemic through local quarantines, he argues that “the evolving nature of the risk means natural pandemics may pose a realistic threat to human civilization.(6).

References for this article can be seen at the Footnotes 3 page on this website (link will open in a new page).

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16. UN shall adopt a ‘one health approach’ integrating veterinary medicine and environmental science to mitigate disease emergence and antimicrobial resistance and to ensure the continuation of agriculture and civilization

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Rapporteur: Laura H. Kahn, MD, MPH, MPP; Research Scholar, Princeton University

One Health is the concept that human, animal, environmental/ecosystem, and atmospheric health are linked. It is a relatively new term but an ancient concept intuitively understood by indigenous peoples around the world. The One Health concept provides a useful framework for analyzing and addressing complex, interdisciplinary problems such as foodborne and waterborne illnesses, antimicrobial resistance, food security, and even climate change.

We live in a microbial world. We need to learn how to live better in it. We need to learn how to sustainably co-exist with the microbes living in us, on us, and around us.

For example, over 7 billion humans and almost 30 billion domesticated animals produce trillions of kilograms of fecal matter that contain billions of microbes. Each year, the massive amounts of fecal matter produced could fill an estimated 1.6 million Olympic-sized swimming pools. According to the World Bank(1), over 2 billion people don’t have access to basic sanitation systems, and almost 9 million of them practice open defecation. Open defecation, as the name suggests, means squatting and defecating out in the open. Many developing countries lack basic sanitation systems for human fecal matter, much less for animal fecal matter which makes up 80 percent of the total fecal matter produced.

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15. WHO shall promote nations’ use of Incident Management System for early detection and response to pandemics

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Rapporteur: Ronald St. John

Basic Premise:

There will be pandemics at some time in the future.

Small outbreaks of infectious diseases occur daily throughout the world. Depending on the transmission potential for specific or unknown pathogens, a small cluster of infected people can rapidly become an epidemic at a local, district/provincial or national level. In the absence of a comprehensive and internationally accepted definition of what constitutes a pandemic, for purposes of this paper, a pandemic is an epidemic that is occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people with a high degree of morbidity and mortality. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127276/

Why are pandemics inevitable?

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