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Epidemics versus pandemics

In a world that has been completely upended in the span of three years by the COVID-19 pandemic, the general public’s knowledge of public health terminology and phenomena has been enhanced dramatically.  Among the trending public health phrases,  “outbreak”, “epidemic”, and “pandemic” are among the most widely cited in everyday conversations and modes of media. According to the Center of Disease Control and Prevention (CDC), “outbreaks” are the most geographically confined of the aforementioned terms; “outbreaks” indicate a sudden increase in the number of cases of a disease in the population of a given geographic location [1].


Similarly, an “epidemic” refers to the, often sudden, increase in the number of cases of a disease in the population of a given (and generally larger) geographic area [1]. Characterized as impacting the largest geographic area of the aforementioned terms, a “pandemic” refers to an epidemic that has spread to numerous countries and continents, often affecting a larger group of people [1]. The COVID-19 outbreak, once restricted to Asia, was classified by the World Health Organization (WHO) as a pandemic on March 11, 2020.


When diseases become expected in the population of a given geographic area by being constantly present or prevalent, they are said to be “endemic”. There is speculation that COVID-19 will soon become endemic in our population. In other words, the COVID-19 virus is not likely to completely disappear. Rather, it is expected that enough individuals within the population will achieve immune protection by vaccination or natural infection. When enough of the population develops immunity, herd immunity is achieved. Herd immunity helps to protect those unable to vaccinate themselves (i.e children or those with medical conditions).


Achieving a state close to herd immunity should lead to lower transmission rates and thus lower hospitalizations and deaths associated with COVID-19 [2]. In time, COVID-19 is expected to become as ubiquitous as seasonal viruses such as the common flu [2]. While it is widely regarded that COVID-19 will become endemic, it is difficult to predict when this will happen. Further, while it was once hoped that herd immunity could be achieved when vaccines became widely available, experts now do not think it likely. Early on in the pandemic, it was theorized that 70-85% of the population must be vaccinated to achieve herd immunity for COVID-19 [3]. And simply put, enough of the population is not vaccinated (and boosted) to achieve herd immunity before the virus mutates.


Widespread awareness of public health principles has also enlisted the general public into a feeling of weariness towards the discovery of any new pathogen. Whereas public health professionals and microbiologists have duteously alerted those willing to listen about the potential of a violent uptick in future pandemics, it is only very recently that these warnings are being heeded seriously by global policymakers. According to public health professionals, the occurrence of pandemics (and the infectious diseases causing them) is likely to increase in coming years for a few reasons. Pandemics are driven by the same human activities associated with climate change and loss of biodiversity, namely: land use changes, agricultural expansion, and wildlife trade and consumption [4].


These human activities result in closer contact between humans, livestock, and wildlife, allowing for quicker transmission of animal microbes to humans; this leads to more infections and thus more outbreaks [4]. These outbreaks occasionally morph into pandemics, with infection spreading globally due to attributes of globalization: improved road networks, densely populated urban centers, and global travel and trade [4]. Thus, whereas the majority of these infections are initiated in developing countries, it does not take long for pathogens to spread around the world - in both developing and developed nations. The rapid nature of global infection was exemplified at the beginning of the COVID-19 pandemic.


Pandemics also underscore a notorious phenomenon in global health: the underprivileged and disadvantaged of society suffer the most - physically, mentally, socially, and financially. While it is obvious that the COVID-19 virus cannot discriminate in infection between the wealthy and poor, it is well-known that societal structures such as race and socioeconomic status and immigration status play a large role in which groups face the worst consequences of the virus. For example, in densely populated India, infection was far more likely to spread in the slums of urban centers, where the poorest residents live. These slums not only lack space to allow proper physical distancing between residents but also lack proper hygiene and sanitation to dispel risk of infection. In the United States, hospitalization and death associated with COVID-19 is far more likely amongst the country’s most disadvantaged populations - poor, BIPOC - because of the high likelihood of pre-existing conditions in these populations. Thus, these already disadvantaged populations are further disadvantaged in health by the COVID-19 pandemic.


It is expected that without a united global front of intervention, pandemics will not only continue to increase in prevalence but also in severity. In the absence of preventative measures, pandemics will: spread more quickly, kill more people, and have a more dire impact on the global economy. Thus, it is crucial for the world to put a concerted effort to reduce, or atleast regulate, the human activities contributing to pandemics. It cannot be a matter of one nation for itself because viruses like COVID-19 do not see national borders.



1. CDC. (2012, May 18). Principles of Epidemiology. Centers for Disease Control and Prevention. Retrieved June 3, 2022, from

2. AHA. (2022). Duke health addresses the COVID-19 endemic and ongoing need for vaccinations: AHA. American Hospital Association. Retrieved June 3, 2022, from

3. Gianola, D. (2020). On the uncertainty about herd immunity levels required to stop COVID-19 epidemics.

4. IPBES. (2020). IPBES workshop report on biodiversity and pandemics. UNEP. Retrieved June 3, 2022, from




Author: Aseelah Saiyed

Editor: Kayjah Taylor

Health Scientist: Aseelah Saiyed




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