These terms, which can be used as nouns and adjectives, are related because they all refer to an
outbreak of a disease. However, the contexts of use differ. Let us take them one by one.
EPIDEMIC
An EPIDEMIC is a large number of cases of a particular disease or medical condition happening at the same time in A PARTICULAR COMMUNITY. It is something affecting or tending to affect a disproportionately large number of individuals within a population, community, or region at the same time.
Examples:
The outbreak of a flu epidemic
An epidemic of measles broke out, and over 200 children died.
Over 500 people died during last year's flu epidemic.
An epidemic of cholera
PANDEMIC
A PANDEMIC is a disease that affects people over A LARGE AREA or ALL OVER THE WORLD. It is an outbreak of a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population.
Examples:
They feared a new cholera pandemic.
One pandemic of Spanish flu took away nearly 22 million lives worldwide.
The intelligence estimate portrays the pandemic as the bad side of globalisation.The 1918 flu was pandemic and claimed millions of lives.
Covid-19 is pandemic and has claimed thousands of lives.
ENDEMIC
An endemic disease is ALWAYS PRESENT IN A PARTICULAR PLACE OR AMONG A PARTICULAR GROUP OF PEOPLE.
Examples:
Malaria is endemic in many hot countries.
The disease is endemic among British sheep.
In conclusion, an epidemic becomes a pandemic when the disease spreads to a wide geographical area or the whole world.
The novel coronavirus disease, COVID-19, started in Wuhan, China, as an epidemic but today, it is a pandemic disease.
Cambridge Dictionary, COLLINS, Dictionary.com , MWD, OALD, LDOCE