The World Health Organization has declared the new coronavirus a pandemic, a decision that comes more than six weeks after the agency said the spread of the disease constituted a public health emergency of international concern.

A pandemic is the worldwide spread of a new disease, according to WHO.

"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," WHO Director-General Tedros Adhanom Ghebreyesus said March 11. "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."

The virus, which causes the respiratory disease COVID-19, has infected more than 121,000 people worldwide and has killed about 4,400, according to Johns Hopkins University's Center for Systems Science and Engineering.

WHO expects to see the number of cases, deaths and countries involved continue to climb.

"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," Tedros said.

Describing the situation as a pandemic does not change WHO's assessment of the threat posed by COVID-19 and what the global agency is doing, and it should not change what countries should do, Tedros said. He noted this is the first time a coronavirus has sparked a pandemic.

"We cannot say this loudly enough, or clearly enough or often enough: all countries can still change the course of this pandemic," Tedros said. "If countries detect, test, treat, isolate, trace and mobilize their people in the response, those with a handful of cases can prevent those cases becoming clusters, and those clusters becoming community transmission."

Even those countries with community transmission or large clusters can turn the tide on this virus, he said.

"The challenge for many countries who are now dealing with large clusters or community transmission is not whether they can do the same, it's whether they will," Tedros said.

Some countries are struggling with a lack of capacity, some with a lack of resources, while others are struggling with a lack of resolve, he said.

"I remind all countries that we are calling on you to activate and scale up your emergency response mechanisms," Tedros said. "Communicate with your people about the risks and how they can protect themselves. This is everybody's business."