Clue: It is worse than an epidemic.
The Merriam-Webster dictionary describes a pandemic refers to 'an outbreak of a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population.'
- First of all there is an outbreak. It happens in one place, in the case of COVID-19 it was Wuhan.
- Then cases spring up elsewhere, in places not geographically connected to the point of outbreak. If enough of these occur it becomes an epidemic.
- When this phenomenon is repeated in a large number of countries across the world - as it has in this case - it can be considered a worldwide phenomenon. It's at this point the outbreak can be characterised as a pandemic.
- COVID-19 is in 114 countries BUT more than 90 per cent of cases were in just four countries and two of those had significantly-declining epidemics
World Health Organization (WHO) Director-General Tedros Adhanom was keen to stress at a press conference in Switzerland on Wednesday that using the word pandemic to describe COVID-19 did not change the level of threat that experts considered the virus to be.
But given the rapid spread of the virus in Europe in recent days - as well as its spread to 114 countries - the definition is unlikely to put anyone's mind at ease.
“Pandemic comes from the Greek word ‘pandemos’, which means everybody," Michael Ryan, the executive director of the Health Emergencies Programme at WHO, told reporters on February 24.
"Pandemos is a concept where there’s a belief that the whole world’s population will likely be exposed to this infection and potentially a proportion of them will fall sick.”
"Pandemic is not a word to use lightly or carelessly," Adhanom said Wednesday.
"It is a word that, if misused, can cause unreasonable fear, or unjustified acceptance that the fight is over, leading to unnecessary suffering and death."
Does the definition change anything?
He was keen to stress that although the disease is now called a pandemic, that will not change the response that countries or global health authorities have to the virus.
"Describing the situation as a pandemic does not change WHO’s assessment of the threat posed by this coronavirus. It doesn’t change what WHO is doing, and it doesn’t change what countries should do," he said.
He also said that while the disease had now spread to 114 countries, more than 90 per cent of cases were in just four countries and two of those had significantly-declining epidemics.
"81 countries have not reported any COVID-19 cases, and 57 countries have reported 10 cases or less. We cannot say this loudly enough, or clearly enough, or often enough: all countries can still change the course of this pandemic," he said
In the 14th century, the Black Death killed between 30% and 60% of Europe's population. And in 1918 the influenza pandemic - known as the Spanish flu, killed around 500 million.
More recent pandemics include swine flu in 2009 and 2010 and HIV, which has killed 32 million worldwide with 770,000 in 2018 alone.