An epidemic usually affecting a large proportion of the population, occurring over a wide geographic area such as a section of a nation, the entire nation, a continent, or the world is called a pandemic.
- The word pandemic comes from the Greek pandemos meaning “pertaining to all people.” The Greek word pan means “all” and the Greek word demos means “people.”
- It is the worldwide spread of a new disease.
- Throughout history, there have been a number of pandemics, such as smallpox, tuberculosis, influenza, etc.
- One of the most devastating pandemics was the Black Death, which killed over 75 million people in 1350.
- The most recent pandemics include the HIV pandemic as well as the 1918, 2009 H1N1 pandemics and COVID-19 pandemics.
- Besides humans, pandemics can also occur in important agricultural organisms (livestock, crop plants, fish, and tree species) or in other organisms.
Features of Pandemics
- Pandemics are usually caused by a novel infectious agent, an infectious agent that is newly capable of spreading rapidly, or both.
- The death toll in a pandemic is generally higher than that in an epidemic. It can also lead to more social disruption, economic loss, and general hardship.
- Increased travel and mobility have increased the likelihood of new diseases spreading.
- Antibiotic resistance increases the risk of future pandemics.
- A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious.
- For instance, cancer is responsible for many deaths but is not considered a pandemic because the disease is not infectious or contagious.
Common Causes of Pandemics
- Pandemic is usually caused by a new virus strain or subtype that becomes easily transmissible between humans.
- Due to bacteria that become resistant to antibiotic treatment.
- Sometimes, pandemics are caused simply by a new ability to spread rapidly, such as with the Black Death.
- Pandemics arise when humans may have little or no immunity against a new virus. Often a new virus cannot spread between people, but if it changes, or mutates, it may start to spread easily. In this case, a pandemic can result.
Effect of Pandemics
Fatality from a pandemic depends upon:
- The number of people who become infected
- The severity of disease caused by the virus (its virulence)
- The vulnerability of affected populations
- The effectiveness of preventive steps
Examples of Pandemic Disease
The Influenza Pandemic
- There are three groups of influenza viruses — A, B, and C.
- Each of these groups can cause illness in humans, but only group A viruses are associated with major epidemics or pandemics.
- Influenza A viruses infect humans and other animals, notably birds and swine.
- Influenza A viruses are continually undergoing evolutionary changes in their two major antigenic constituents – hemagglutinin (H) and neuraminidase (N).
- There are 16 H strains and 9 N strains of influenza A viruses currently recognized.
- The viruses are named according to their H and N components, as well as the location where they were originally isolated.
- The evolutionary changes in H or N (drift) may result in a sufficiently changed antigenic structure that immunity from prior infections may not protect all those who come in contact with it, contributing to annual epidemics.
- In addition, simultaneous infection with two different influenzas A viruses (in humans or other animals) may result in a reassortment of H and N components — antigenic shift — giving rise to a novel strain against which no one has immunity. I
- In this circumstance, pandemics of influenza may occur.
The World Health Organization (WHO) provides an influenza pandemic alert system, with a scale ranging from Phase 1 (low risk of a flu pandemic) to Phase 6 (a full-blown pandemic):
- Phase 1: A virus in animals has caused no known infections in humans.
- Phase 2: An animal flu virus has caused infection in humans.
- Phase 3: Sporadic cases or small clusters of the disease occur in humans. Human-to-human transmission, if any, is insufficient to cause community-level outbreaks.
- Phase 4: The risk for a pandemic is greatly increased but not certain.
- Phase 5: Spread of disease between humans is occurring in more than one country of one WHO region.
- Phase 6: Community-level outbreaks are in at least one additional country in a different WHO region from phase 5. A global pandemic is underway.
- Park, K. (n.d.). Park’s textbook of preventive and social medicine.
- Hennekens CH, Buring JE. Epidemiology in Medicine, Lippincott Williams & Wilkins, 1987.