An epidemic is an unexpected rise in cases within a community or region, which could mean part of a country, an entire country, an ethnic group spread across multiple countries, or an entire landmass. And a pandemic is an epidemic that has exponential growth.

An epidemic usually starts within a particular country and if it becomes a pandemic it will grow rapidly and spread to other countries, but the WHO definitions are only based on the number of cases compared to normal and how fast the number of cases is rising.