COVID-19 Pandemic

Explained: The difference between endemic, epidemic and pandemic

Published : December 31, 2021 13:38 IST

If SARS-CoV-2 becomes endemic it must not neccessarily become less dangerous, but it may. Photo: picture-alliance/M. Schönherr

Many virologists assume the coronavirus will become endemic and we will have to live with it, especially since omicron.

Endemic: the constant threat

A disease that occurs regularly in certain regions is called endemic. When a disease becomes endemic, the number of people falling ill remains relatively constant over time. The number of cases is higher than in other areas, but does not increase over time. Over a certain period of time, approximately the same number of people contract the disease, again and again. A typical example is malaria, which affects 300 million people worldwide every year, mainly in the tropics.

As early as May 2020, the World Health Organization (WHO) predicted that the coronavirus could become an endemic virus. The delta and omicron variants have since shown how adaptable the virus is , similarly to the flu. That means it is out there in the world. We have to learn to live with it in certain regions around the world. It will not disappear.

Epidemic: only in one region

An epidemic is spoken of when a disease occurs with unusual frequency in a certain region and in a limited period of time. When the number of cases of disease in that particular region rises above the normal expected (endemic) level, it is called an epidemic. When the disease incidence is localized, it is often referred to as an outbreak. An epidemic occurs, for example, when the virulence of a particular pathogen changes: A virus mutates and becomes more contagious. Epidemics can also occur when diseases are newly introduced into a certain area. The prerequisite is that a disease can be passed from person to person.

An example of this is smallpox, which was introduced to the Americas via the arrival of Europeans from the beginning of the 16th century. Because the indigenous population had never been in contact with the pathogens before, their immune systems were not equipped to fend off the virus. Individual projections suggest that up to 90 per cent of the indigenous population of the Americas fell victim to smallpox.

Pandemic: worldwide spread

If a disease spreads not only regionally, but across countries and continents, experts refer to it as a pandemic. This means, above all, that successful control of the disease depends on cooperation between the health systems of different countries. It does not mean that a disease is particularly dangerous or deadly.

According to the WHO and the U.S. national health agency, the Centers for Disease Control and Prevention (CDC), pandemics are usually caused by newly emerging pathogens or virus types. These can be zoonoses, for example — diseases that are transmitted from animals to humans. If a disease is new to humans, very few people will be immune to the virus. Vaccinations are also not available in this case. This can lead to very large numbers of people becoming ill. How dangerous or fatal the disease is depends on the specific virus and the health of the individual.

Even if, in percentage terms, a disease is harmless in most cases, the absolute number of serious illnesses during a pandemic can be very high. This is simply because a very, very large number of people are infected with the pathogens overall. A typical disease that repeatedly assumes pandemic proportions is influenza. The 1918 influenza pandemic, also known as the Spanish flu, killed 25 to 50 million people, more than in World War I. Swine flu also triggered a pandemic in 2009. However, even during a pandemic, individual isolated areas can be spared from the disease, for example, island or mountain areas. Air travel, however, favors the spread of pandemics.

'Epidemics' that are not the real thing

The terms epidemic and pandemic normally refer to infectious diseases. However, because it conveys a need for urgent action, noncommunicable diseases or unhealthy habits are sometimes referred to as epidemics as well. Strictly speaking those formulations are essentially metaphoric: "Diabetes epidemic" or "opioid epidemic", for example. The term has even been used to describe the increase of criminal behavior in society with media referring to an "epidemic of rape". However, it has been noted by some that this misuse of the word distracts from the responsibility of the perpetrators.