After weeks of resisting mounting pressure from scientists, politicians and others, the World Health Organization in Geneva has decided to describe the coronavirus outbreak as a pandemic.

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The declaration comes after a 13-fold rise in the number of cases outside of China and a trebling of countries affected in the last two weeks — but does not change WHO strategy for tackling spread of the virus, director-general Tedros Adhanom Ghebreyesus said in an 11 March press briefing.

“WHO has been assessing this outbreak around the clock and we are deeply concerned both by the alarming levels of spread and severity, and by the alarming levels of inaction,” said Tedros Adhanom Ghebreyesus.

“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,” Tedros said. “Pandemic is not a word to use lightly or carelessly. 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.”

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Many scientists had been calling for the change in language for weeks — after large outbreaks were detected in South Korea, Iran and Italy. At the time, some researchers suggested that countries would soon move from efforts that involve containing as many new cases as possible to social-distancing measures, such as school closures, that do not rely on knowing who is infected with the virus and who is not.

The virus is now in more than 100 countries. It has infected some 120,000 people, killing more than 4,000 of them. Several nations have closed schools in a bid to stop the virus, and Italy has entered an unprecedented countrywide lockdown.

“This is not just a public health crisis, it is a crisis that will touch every sector — so every sector and every individual must be involved in the fight,” said Tedros.

Researchers have been working rapidly since the outbreak came to light in January to characterize the virus, work out why it is so infectious, find out where it came from, and help with diagnosing infections.