What is a pandemic?

Disease experts use a scale of terms: an outbreak is a sudden rise in cases in one area, an epidemic spreads widely in a region, and a pandemic spreads worldwide. Pandemics usually involve a pathogen to which most people have little or no immunity, such as a new influenza strain or coronavirus. The World Health Organization declared COVID-19 a pandemic on 11 March 2020. History records many devastating pandemics, including the Black Death of the 14th century and the 1918 influenza, which infected about a third of the world population. The word comes from Greek, meaning all the people.