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Explained: When does a disease become endemic?

According to an article published in the journal Science, when epidemics become endemic, the responsibility of protecting against it shifts from the government to the individual.

By: Explained Desk | New Delhi |
Updated: May 16, 2020 7:43:31 pm
Explained: When does a disease become endemic? An illustration of the novel coronavirus. (Getty Images)

A top official of the World Health Organization (WHO) Wednesday said that like HIV, the novel coronavirus could become endemic and “may never go away”, and urged for a “massive effort” to contain the spread of COVID-19.

“It is important to put this on the table: this virus may become just another endemic virus in our communities, and may never go away,” Dr Mike Ryan, WHO emergencies director said during a press briefing.

Dr Ryan noted that even if a vaccine was found, coping with the disease would require a “massive effort”. As of now, more than 4.4 million cases of the disease have been recorded worldwide and more than 300,000 have died.

What is an endemic disease?

According to the US Centers for Disease Control and Prevention (CDC), a disease is endemic when its presence or usual prevalence in the population is constant. When the cases begin to rise, it is classified as an epidemic. If this epidemic has been recorded in several countries and areas, it is called a pandemic.

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Some examples of endemics include the chicken pox and malaria, where there are predictable number of cases every year in certain parts of the world.

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A 1948 definition of endemic cholera cited in the Indian Journal of Endocrinology and Metabolism defines it as: “An endemic area is one in which over a number of years, there is a practically continuous presence of clinical cholera with annual seasonal exacerbation of incidence.”

The dictionary of epidemiology defines an endemic disease as, “the constant presence of a disease or infectious agent within a given geographic area or population group; may also refer to the usual prevalence of a given disease within such an area or group.”

What happens when a disease becomes endemic?

According to an article published in the journal Science, when epidemics become endemic, they become “increasingly tolerated” and the responsibility of protecting against it shifts from the government to the individual. This means, rather than government agencies actively engaging in tracking and identifying cases, the individuals themselves will be responsible for managing risk from the disease and seeking care.

Further, the sociopolitical response to the disease may also change, with investment in the disease becoming institutionalised along with the disease-inducing behavioural changes in people. Once people become aware of the risks of infection, they will alter their behaviour and mitigate the consequences.

The article states “epidemic diseases typically have higher mortality and morbidity than endemic diseases, owing to lack of clinical experience and knowledge, as well as innate pathogenicity. Over time, effective prevention and treatment interventions emerge.”

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When does a disease become endemic?

One mathematical modelling published in the Journal of Epidemiology and Community Health states that if R0, which is the rate at which the virus is transmitted is equal to 1, then the disease is endemic. When R0>1, it implies that the cases are increasing and that the disease will eventually become an epidemic. If R0<1, it implies the number of cases of the disease are decreasing.

Here, R0 refers to the number of people infected by a person who has the disease.

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