The World Health Organization has announced the worldwide pandemic of the Covid-19 coronavirus.
According to the WHO definition, a pandemic is "the worldwide spread of a new disease."
It occurs when a new virus appears and spreads around the world, and most people are not immune to it.
Pandemics we knew already: smallpox in 19th century, plague in 14th century, cholera (periodically in 19th century, also once in 20th century).
We also know about outbreaks cases of pandemic of typhus, leprosy and malaria.
There have been several influenza pandemics in the world: Spanish flu in 1918-1920 and swine flu in 2009-2010. The death toll from Spanish flu was estimated in millions, with more than 2,000 deceased from swine flu.
According to WHO Director-General Tedros Ghebreyesus, "this is not just a public health crisis, it is a crisis that will touch every sector."