What is a pandemic?

Declaring a pandemic has nothing to do with changes to the characteristics of a disease, but is instead associated with concerns over its geographic spread. According to the World Health Organization, a pandemic is declared when a new disease for which people do not have immunity spreads around the world beyond expectations. How does the WHO decide whether to call it a pandemic? Cases that involve travellers who have been infected in a foreign country and have then returned to their home country, or who have been infected by that traveller, known as the “index case”, do not count towards declaring a pandemic. There needs to be a second wave of infection from person to person throughout the community. Once a pandemic is declared, it becomes more likely that community spread will eventually happen, and governments and health systems need to ensure they are prepared for that. An epidemic, on the other hand, is a sudden increase in cases of an illness or disease that can be unique to one country or community.

Source: TheGuardian