An epidemic is an outbreak that spreads quickly among many people in a population; a pandemic is an outbreak that has spread across countries or continents. A memory hook: pandemic comes from Greek for all the people, so think pan for panoramic, wide reach, while epidemic simply means among the people, without that wider geography built in.
The core difference
Scale is the core difference: epidemic describes a fast-spreading outbreak within a population, while pandemic describes one that has spread across countries or continents.
- epidemic — an outbreak of disease spreading quickly and affecting many people at once: The city imposed travel restrictions to slow the epidemic.
- pandemic — an outbreak that has spread across countries or continents: The COVID-19 pandemic changed how people work and travel.
- epidemic — also used figuratively for a sudden rise in something harmful: Officials described the rise in overdoses as an epidemic.
How to tell them apart
The two words trace a difference in Greek. Epidemic comes from epidemios, among the people, built from epi- (upon) and demos (people) — it describes something happening within a population. Pandemic comes from pandemos, of all the people, from pan- (all) and demos, which points to a much wider reach.
In practice, an outbreak often starts as an epidemic and is reclassified as a pandemic once it crosses into multiple countries or continents, which is exactly what happened with the 1918 flu and, more recently, COVID-19.
