What are epidemic, pandemic and endemic?

As India’s daily coronavirus cases dipped below the 15,000 mark, the Director of All India Institute of Medical Sciences, Randeep Guleria, said the country is currently witnessing the “tail” of the third wave and Covid-19 will gradually become endemic.

On March 11, 2020, the World Health Organization had declared Covid-19 outbreak a global pandemic after a rapid increase in the number of cases outside China. 

Covid-19 was an epidemic in China before it turned into a global pandemic. So let us now understand the differences between an epidemic and a pandemic and when a disease is considered to be endemic. 

The US Centers for Disease Control and Prevention (CDC) describes an epidemic as an often sudden increase in the number of cases of a disease above what is normally expected in that population in a specific geographical area. Outbreak carries the same definition but is used for a more limited geographic area.

An epidemic may result from a change in the virulence of a particular pathogen. For example, a virus becomes more contagious after mutation. Diseases that are newly introduced into a certain area can also cause epidemics

An epidemic of an infectious disease that has spread over several countries or continents is called a pandemic. 

The World Health Organization declares a pandemic when the spread of a disease is exponential. The deciding factor for a disease to be called a pandemic is not its severity but the extent to which it has spread.

Pandemics can claim millions of lives and ravage economies. It is usually caused by new pathogens and these could be zoonotic in nature, transmitting from animals to humans.

Such new pathogens or viruses infect people easily and spread person to person in an efficient and sustained way. Because the virus is new to humans, very few people will have immunity against the pandemic virus, and a vaccine might not be widely available. 

Past pandemics include AIDS, 2009 swine flu pandemic and the 1918 Spanish flu pandemic.

Meanwhile, a disease is said to be endemic when it shows a constant presence within a geographic area. The amount of a particular disease that is usually present in a community is referred to as the baseline or endemic level of the disease. 

For instance, Malaria is considered endemic in certain countries. WHO has predicted that coronavirus could become an endemic virus.

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