The World Health Organisation (WHO) declared the novel coronavirus strain Covid-19 a pandemic on March 11.
"We have called every day for countries to take urgent and aggressive action. We have rung the alarm bell loud and clear," said Tedros Adhanom Ghebreyesus, the WHO chief.
"All countries can still change the course of this pandemic. If countries detect, test, treat, isolate, trace and mobilise their people in the response," he said.
"We are deeply concerned by the alarming levels of spread and severity and by the alarming levels of inaction."
Here's what the difference between an epidemic and a pandemic is.
What is a pandemic?
The WHO defines a pandemic as the worldwide spread of a new disease, across several countries or continents, affecting a large number of people.
A viral outbreak could be categorised as a pandemic if it is markedly different from recently circulating strains, and if humans have little or no immunity to it, according to the UK’s Health and Safety Executive.
What is an epidemic?
In contrast, an epidemic refers to a more localised or regional outbreak of a disease, rather than one that has spread across the globe.
It is an increase - often sudden - in the number of cases of a disease that is above what is normally expected in that population in that area, according to the Centers for Disease and Control Prevention (CDC).
The CDC explains that an epidemic may result from:
A recent increase in amount or virulence of the agentThe recent introduction of the agent into a setting where it has not been beforeAn enhanced mode of transmission so that more susceptible persons are exposedA change in the susceptibility of the host response to the agentFactors that increase host exposure or involve introduction through new portals of entry
Why so long to declare pandemic?
Though the disease spread beyond China in January, WHO have refrained from describing the disease as pandemic until now.
That's because the virus spread beyond the origin country had not yet been sustained for a significant amount of time.
Now that the disease is spreading from person to person within countries outside of China, rather than affecting people who had recently visited the affected are it can be classed as pandemic.