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The World Health Organization (WHO) describes a pandemic as the “worldwide spread of a new disease”. Often there is little to no immunity within a community to this new or re-emergent disease, so transmission and contraction is significant. While a general definition of ‘pandemic’ exists, the term is often misapplied. However, there are characteristics of disease and disease spread that allow public health practitioners to identify a pandemic and begin response.
David Morens, Gregory Folkers, and Anthony Fauci published a paper in a 2009 volume of The Journal of Infectious Diseases describing the eight characteristics of a pandemic. They note that pandemic is often used by the media to describe disease spread which does not rise to the level of being classified by scientists and public health officials as pandemic. These are the eight characteristics that are common in diseases that are officially classified as pandemics:

1. Wide Geographic Extension
Pandemics impact a wide geographic area, often being classified as transregional, interregional, or global.

2. Disease Movement
The spread of a pandemic disease can be traced from place to place.

3. High Attack Rates & Explosiveness
Refers to the number of cases of a particular illness reported within a short time frame. Diseases with slow rates of transmission are rarely classified as a pandemic, as was seen in the 1999 spread of the West Nile virus from the Middle East to both Russia and the Western Hemisphere.

4. Minimal Population Immunity
While pandemics have occurred in partly immune populations, limited population immunity has created ideal conditions for pandemic disease to develop and spread.

5. Novelty
The term ‘pandemic’ is often applied to new diseases, or new variants of known diseases. However, this does not preclude repeatedly

6. Infectiousness
Pandemic diseases generally have a high level of infectiousness. While the term has been applied to non-infectious health issues, such as cigarette smoking, this term is often used in less scientific settings.

7. Contagiousness
Most diseases classified as ‘pandemic’ are transferred from person-to-person.

8. Severity
Pandemic typically describes diseases that are severe or fatal, such as SARS, HIV/AIDS, and the Black Death. Measuring Magnitude

In the event of a pandemic, the WHO and the U.S. Center for Disease Control and Prevention (CDC) direct response efforts. Depending on the severity of the outbreak, local or national public health agencies may also respond. The World Health Organization breaks pandemic alerting into five phases:

  • Phase 1: No viruses circulating among animals have been reported to cause infections in humans
  • Phase 2: Animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a potential pandemic threat.
  • Phase 3: An animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. Limited human-to-human transmission may occur under some circumstances
  • Phase 4: Characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks.” The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic.
  • Phase 5: Characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.
In addition to the current COVID-19 Pandemic, the Kentucky Cabinet for Health and Family Service explains that there have been four other pandemics in United States in the last 100 years: the 1918-1919 Spanish Flu, the 1956-1958 Asian Flu, the 1968-1969 Hong Kong Flu, and the 2009 Novel H1N1. Combined, these four pandemics have claimed thousands of lives in the Commonwealth, hundreds of thousands in the United States, and millions worldwide. Spanish Influenza 1918-1919
Historical examples of pandemic demonstrate that while a pandemic may be devastating to a community from a life safety and economic standpoint, the threat was often downplayed and ignored. The 1918 Spanish Influenza pandemic was initially disregarded as having a significant impact because influenza was thought of as a minor illness that incapacitated the sick for a relatively short period of time before they eventually recovered. However, as the Spanish Influenza rose to pandemic level, it redefined the public’s perception of the virus. A historian at the time noted that at a military encampment in southern Ohio, soldiers would arrive healthy and within twenty-four hours would be dead from the flu.

The virus spread globally along trade routes and shipping lines. Residents of North American, Europe, Africa, Asia, Brazil, and the South Pacific were particularly affected by the illness, which in-total infected 1/5 of the global population. In contrast to the majority of flu strains, the Spanish Influenza primarily affected young, healthy adults between the ages of 20 and 40. The mortality rate was 2.5%, an astounding figure given that flu outbreaks typically have a rate of 0.1%. By the end of the pandemic, the virus had claimed 20 million lives worldwide and 675,000 in the United States.

Asian Flu 1956-1958
The New York Times first broke the news of the Asian Flu in 1957 when they published a story of a flu virus that had infected 250,000 in Hong Kong. Months after this story was published, the disease had spread to the United States. Unlike Spanish Influenza, the Asian Flu was most commonly reported in the vulnerable populations, such as the elderly and individuals with heart and lung conditions. People with rheumatic heart disease and women in their third trimester of pregnancy were uniquely impacted. Infection for this pandemic came in two parts—the first in the late summer of 1957 and the second in the winter of 1958. The death toll for the Asian Flu widely varies, with sources reporting between 1 and 4 million deaths worldwide and approximately 69,800 in the United States.

Hong Kong Flu 1968-1969
The Hong Kong Flu is the mildest of all pandemics of the 20th century, a fact that is often explained by its similarity to the Asian Flu which increased immunity to the 1968 strain and the fact that it hit the United States in late December when most students were on break, reducing opportunities for spread. As with the Asian Flu, the vulnerable populations, particularly the elderly, were most at risk. By the end of the pandemic in 1969, it had claimed 33,800 lives in the US.

H1N1 2009-2010
This pandemic first appeared in the United States in the spring of 2009. By June, H1N1 had infected 18,000 people in the US. The virus primarily affected the populations most typically affected by the flu: children and infants, pregnant women, the elderly, and individuals with prior-existing health conditions. Due to advancements in medical research and technology, the overall impact of the pandemic was curbed. A vaccine was introduced in the fall of 2009. Approximately 80 million people were vaccinated worldwide. By the time the pandemic was declared over in the spring of 2010, between 43-89 million people had been infected and between 8,870 and 18,300 people had died.

COVID-19 2020-present
The most recent pandemic first appeared in the United States in the spring of 2020. By July 2020, COVID-19 had infected over 200,000 people worldwide. The virus initially primarily affected the elderly, and individuals with prior-existing health conditions, however as spread increased so did the populations at-risk. A vaccine was approved for use against the virus in December of 2020, with hopes that the pandemic will be declared over in 2021.
Pandemics typically have a warning time of months to years and pose the following potential impacts:

People
Farmers-pandemic could affect crop production & yield since they could not seed or harvest; General populace -would be impacted due to both physical and psychological impacts of disease; Possible school closures would aid in disrupting spread of disease; Vulnerable populations may experience more impacts due to synergistic effects of pandemic symptomology.

Economy
Pandemic can cause business slowdown or even recession; decreased food and merchandise shipped throughout area would increase cost; loss of buyers and sellers due to potential risk of contagion. Increased staff absences (upwards 50% workforce may require time off over entire period of pandemic).
< br/> HealthCare System
Increased emergency clinical care visits, more hospitalization (upwards 1-4% symptomatic patients will require hospitalization) leading to severe and overwhelming impacts on healthcare and public health system; workforce absences leading to minimal patient care

Natural and Man-Made Environment
Potential increased loss of agricultural assets (crop & livestock) due to loss of manpower to harvest crop; fewer livestock and crop markets due to restriction of crowds which prevent spread of pandemic disease; Infrastructure could be impacted due to lack of repair and upkeep if pandemic is extensive and lengthy; Utility lines and repairs would take longer to repair due to manpower lost.
The 2016 Global Risk Report published by the World Economic Forum has proposed that climate change could be a causal factor in future pandemics. This finding is further explored in a 2016 report produced by Johns Hopkins University’s School of Advanced International Studies, Pandemics in a Changing Climate – Evolving Risk & Global Response. The report explains that vector ecology indicates the potential for climate change to create the conditions for future pandemics. Changes in temperature, precipitation, and pH levels due to climate change will impact the quantity and quality of ecological services, such as food, water, and soil. Ecosystem shifts can impact the migratory patterns, habitats, population, and survivability of certain animal and insect populations. Such changes may increase human-animal or human-insect contact, increasing the likelihood of transmission. For example, as hot summer months extend tick and mosquito populations, both culprits in transmission of epidemic-causing viruses, can survive longer and have more opportunities to infect humans. Climate change may have more direct impacts on humans by making certain populations, particularly in developing countries, more susceptible to illness by creating food and water security crises.