Outbreaks of disease are common, but they can vary drastically in severity. While an outbreak is merely an increase in the number of cases of a disease, an epidemic is when an infectious disease spreads rapidly to a large population. This is different from a pandemic, where an infectious disease spreads around the globe.
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What is an epidemic?
Epidemics tend to be considered on a more local scale and affect a limited, but significant, population. Typical death tolls for epidemic cases of influenza lie at around 21,000 lives. Epidemics can occur quite regularly, with annual or almost annual epidemic outbreaks of influenza.
One of the more famous epidemics in recent times was the 2003 SARS epidemic in the middle east, which claimed the lives of nearly 800 people. Epidemic outbreaks of influenza can occur much more regularly. Epidemics can occur within pandemics, as a way of dividing different focus areas. For example, by March 2020, COVID-19 had three epidemic foci.
How does a pandemic differ from an epidemic?
The main way pandemics differ from epidemics is through the breadth of their reach. They cover wider geographical areas, often the entire world, and affect far more people than an epidemic. Similarly, pandemics tend to cause many more deaths than epidemics. All in all, this often creates significant social disruption, economic loss, and hardship in general.
One of the determining factors in what turns an outbreak into a pandemic is how infectious it is. Pandemics are usually caused by new viruses or new strains of viruses, which are unknown to most immune systems because they have not circulated in a long time. This differs from epidemics, which often occur annually, and enables them to spread quickly between people.
Influenza in 1918-1919, also known as Spanish influenza, is an example of a very deadly pandemic in recent history. It is estimated to have killed between 20-50 million people. Other, more recent examples, include the 2009 H1N1 influenza and COVID-19 2019-present.
How do epidemics and pandemics compare?
Much of the research directly comparing epidemics and pandemics focus on influenza, because it occurs regularly as epidemics and will on some rare occasions manifest as a pandemic. However, a study of influenza epidemics and pandemics in the 20th century noted that it can be difficult to compare epidemics and pandemics, due to variability in seasons and the virulence of different strains.
Epidemics and pandemics can influence each other, occasionally. One study looking at the pattern of mortalities in influenza epidemics and pandemics found that older people, above the age of 65, accounted for a high proportion of initial deaths in influenza pandemics, but the proportion of elderly deaths quickly declined in the decades following the pandemic. The risk of death from an influenza epidemic following a pandemic decreased between 7-fold and 28-fold.
Epidemics present fewer disturbances to everyday life, whereas pandemic preparation has been advocated for since the 20th century’s pandemics. Public health experts say, and did before COVID-19, too, that it is a question of when a pandemic occurs, rather than if. Some of the preparations people can undertake are to create a plan based on their risk groups, such as ensuring a way to still obtain prescription medicines and food.
From the perspective of relevant authorities, controlling a pandemic can be extremely hard compared to an epidemic. As has been seen during the current COVID-19 pandemic, pandemics require more detailed calculations on patients requiring hospitalization, how many hospital beds are available, and other equipment-related calculations.
There are also several response measures to consider during a pandemic or epidemic, such as case and contact finding, containing infected individuals, and measures to prevent infection in health facilities, nursing homes, and/or long-term care facilities.
However, many places in the world can also be massively at risk from epidemics – if public health measures, such as clean water and handwashing etiquette, are not possible, epidemics can spread rapidly in that population. Similarly, these places are more at risk during pandemic preparations because there may not be facilities to adequately test for diseases.
Although it should be noted, inadequate testing capacity was a global trend during the COVID-19 pandemic, which was perhaps also symptomatic of general lack of preparation globally.
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- Association of Professionals in Infection Control. 2020. Outbreaks, Epidemics, and Pandemics—What You Need To Know. [online] Available at: <https://apic.org/monthly_alerts/outbreaks-epidemics-and-pandemics-what-you-need-to-know/>
- Simonsen, L., Clarke, M., Schonberger, L., Arden, N., Cox, N., and Fukuda, K., 1998. Pandemic versus Epidemic Influenza Mortality: A Pattern of Changing Age Distribution. Journal of Infectious Diseases, 178(1), pp.53-60.
- Bedford, J., Enria, D., Giesecke, J., Heymann, D., Ihekweazu, C., Kobinger, G., Lane, H., Memish, Z., Oh, M., Sall, A., Schuchat, A., Ungchusak, K. and Wieler, L., 2020. COVID-19: towards controlling of a pandemic. The Lancet, 395(10229), pp.1015-1018.