Difference between pandemic, epidemic and endemic

The March 11 of 2020, World Health Organization (OMS) declared covid-19 a pandemic. Since then, this word has accompanied us daily to contextualize terms such as Sars-Cov-2, variants, omicron, delta, antigens, PCR... A language more typical of scientific environments than domestic ones.

Two years later, the pandemic is still with us. Maybe because the omicron variant has become predominant or because of boredom that generates a crisis so prolonged in time, since People are beginning to talk about when we could overcome the pandemic or whether or not covid could become endemic. However, based on the definitions of these terms, it does not seem that we are yet at the point necessary to change levels.

What is a pandemic?

According to Nacho de Blas, researcher in Veterinary Epidemiology and professor at the University of Zaragoza, in the epidemiological field -Diseases are classified according to their temporal evolution. That is, depending on the number of cases registered in a period of time. There are two main groups: the epidemic and the endemic.

Throughout the 20th century, humanity has lived other pandemics like that caused by the virus influenza A (H1N1) and that has gone down in history as the Spanish flu (1918). Coming from the United States, it spread through Europe, Africa and much of Asia and Oceania during the First World War. In 1957, there was another flu pandemic, the H2N2, originally from Asia. The Hong Kong flu (H3N2) occurred in 1968, although it had a smaller extension. In 1983 the HIV causing AIDS and 2009, a new variant of influenza A It spread throughout the world from Mexico.

What is an endemic?

The second large group is that of endemic diseases. These are with us always, but Their prevalence is low and they suffer seasonal peaks. These moments of peak of the disease can be due to a change in temperatures (like it happens in winter with the flu) or because they are vector transmission and the ideal conditions for its transmission are met. This is what happens, for example, with the malaria In certain African regions, it is transmitted through the bite of mosquitoes, which are more prevalent in times of heat and humidity.

In her Etymological origin We also found some keys to differentiate the epidemic from the endemic. Thus, they come from the Greek terms 'epidemeo' (visit) and 'endemeo' (reside). That is to say, While the former visit us periodically with abrupt peaks, the latter reside among us.

According to Nacho de Blas, it is difficult for covid to still become an endemic disease. “It will most likely present itself in a mixed way,” He clarifies, "the virus is still with us but it remains in a kind of balance that when it is broken, in winter for example with the flu, there is a sharp increase in cases, only to return over time to a stable proportion."

In addition to these two large groups, diseases occur in a different way. hyperendemic: high prevalence and propensity in a population (does not occur in humans); sporadic: the disease manifests itself in specific and irregular outbreaks and affects few individuals; anademic: when sporadic peaks occur and it is not transmitted from sick to healthy (like salmonellosis, the infection is contracted through poisoning).

In any case, Diseases follow a series of processes and covid is not exempt from them. After an epidemic outbreak (in Wuhan in 2019) it became a pandemic, over time a mutual adaptation will occur between the virus and humans, which will allow the evolution of the disease to an endemic or mixed form to finally pass in a sporadic manner.