The World Health Organization announced on Wednesday that COVID-19 has now been officially categorized as a pandemic

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The coronavirus has officially become a pandemic, according to the World Health Organization.

During a media briefing led by director-general Tedros Adhanom Ghebreyesus on Wednesday, the agency announced that after “assessing this outbreak around the clock” and feeling “deeply concerned both by the alarming levels of spread and severity, and by the alarming levels of inaction,” the WHO has “made the assessment that #COVID19 can be characterized as a pandemic.”

To get a sense of what this means and why the virus has reached pandemic levels, here is a break down of everything you need to know.

What is a pandemic?

A pandemic is “the worldwide spread of a new disease,” for which people do not have immunity, that has spread globally at an alarming speed and an alarming level of severity, according to the WHO. “Viruses that have caused past pandemics typically originated from animal influenza viruses,” the organization further explains on their website.

What happens during a pandemic?

While situations can vary, the WHO explains that both seasonal and pandemic influenza can infect people of all ages and “most cases will result in self-limited illness in which the person recovers fully without treatment.” However, seasonal influenza, or the flu, can typically be more deadly among the elderly or people with existing medical conditions.

Why is the coronavirus considered a pandemic?

Prior to the official announcement, the WHO’s Ghebreyesus explained, “In the past two weeks, the number of cases of #COVID19 outside China has increased 13-fold & the number of affected countries has tripled. There are now more than 118,000 cases in 114 countries, & 4,291 people have lost their lives.”

“Thousands more are fighting for their lives in hospitals. In the days and weeks ahead, we expect to see the number of #COVID19 cases, the number of deaths, and the number of affected countries climb even higher,” he continued.

Ghebreyesus also warned that “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.”

The WHO says that despite “describing the situation as a pandemic,” it “doesn’t change what WHO is doing, and it doesn’t change what countries should do,” before emphasizing that “all countries can still change the course of this pandemic” if they continue to “detect, test, treat, isolate, trace, and mobilize their people in the response.”

The organization also urges all countries to “strike a fine balance between protecting health, minimizing economic & social disruption & respecting human rights,” seemingly referencing the rise in reports of racists attacks against asians amid concerns about the global outbreak.

What is the difference between a pandemic, epidemic and endemic?

An endemic refers to the “constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area,” according to The Centers of Disease Control and Prevention. An epidemic is “an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area,” while a pandemic is “an epidemic that has spread over several countries or continents, usually affecting a large number of people.”

When was the last global pandemic?

In 2009, WHO declared the outbreak of H1N1 influenza a global pandemic. At the time, H1N1 was referred to as the “swine flu” because the virus showed similar genes to influenza viruses that occurred in pigs in North America, according to the CDC.

The organization states that from April 2009 to April 2010, approximately 60.8 million cases, 274,304 hospitalizations and 12,469 deaths occurred in the United States as a result of the H1N1 pandemic. A recent update from the organization also says that the virus “is now a regular human flu virus and continues to circulate seasonally worldwide.”

Other notable pandemics include the on-going global HIV/AIDs pandemic, which killed an estimated 2.8 million people in 2005 alone, and the 1918 Influenza pandemic (dubbed “The Spanish Flu” even though the virus did not originate in Spain), which killed at least 50 million people worldwide while it ran its course. The “Spanish flu” has been called one of the deadliest pandemics in history.

“Someone’s grandmother remembered coming out and wondering why all her neighbors were sleeping on their lawns,” Mütter museum manager Nancy Hill told The New York Times in March 2020 to explain just how deadly the pandemic was at the time.

“It wasn’t until she was older that she realized that they were all dead,” Hill added.