A mysterious pneumonia outbreak that originated in China is linked to a virus that has never been seen before. Scientists have identified the virus as a new type of coronavirus, reports the World Health Organization (WHO). After being called the 2019 novel coronavirus or 2019-nCoV for weeks, the disease caused by the virus was officially named COVID-19 by the WHO in mid-February.

Most coronaviruses cause mild to moderate symptoms like the common cold, according to the Centers for Disease Control and Prevention (CDC). But coronaviruses are the same family of viruses that include severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS).

SARS was first recognized in China in November 2002. It killed 774 of the 8,098 people infected, according to the CDC. It spread to more than two dozen countries including the U.S. and Canada before it was contained.

"There is a strong memory of SARS, that's where a lot of fear comes from, but we're a lot more prepared to deal with those types of diseases," Dr. Josie Golding, from the Wellcome Trust, a London-based research charity, tells the BBC.

The coronavirus COVID-19 in yellow is seen emerging from cells (blue and pink) cultured in a lab. This scanning electron microscope image shows the new coronavirus in yellow emerging from cells (blue and pink) cultured in a lab. (Photo: NIAID-RML [CC BY 2.0]/Flickr)

Researchers are still working to learn more about the mysterious illness. Here's what we know so far.

Where did it come from?

This image from the CDC depicts the 2019 novel coronavirus This image from the CDC depicts the 2019 coronavirus. The spikes along the outer surface of the virus give it its crown, or corona. (Photo: CDC)

The strain has been linked to a seafood market in Wuhan, China, that has been closed for sanitation since Jan. 1. Local media outlets have reported that the market also sold snakes, marmots, monkeys and other animals. This sparked concerns that the virus was transmitted from animals to humans.

Researchers are trying to determine the origin of the virus. At times, various scientists have said that it may have originated from snakes, bats or pangolins.

Is it serious?

Medical staff transfer patients to Jin Yintan hospital on Jan. 17, 2020 in Wuhan, China. Medical staff transfer patients to Jin Yintan hospital in January 2020 in Wuhan, China. (Photo: Getty Images)

So far, more than 4,700 people have died from the coronavirus. Since the virus was first detected in China on Dec. 12, more than 127,800 cases of COVID-19 have been diagnosed. That's far more than the 774 deaths and about 8,000 cases diagnosed during the 2003 SARS outbreak.

Li Wenliang, a doctor working in Wuhan, was one of the first to warn about the coronavirus outbreak on Dec. 30. Silenced by the police, he later became infected with the virus and died, according to The New York Times.

In early February, two newborn babies were infected in China, reports CNN. It may be a case where the mothers infected the child in utero or they were exposed through handling by an infected health care work or handling or breastfeeding by the mother.

Infectious disease experts were initially cautious about using the word "pandemic." A pandemic is the worldwide spread of a new disease, according to WHO.

But WHO declared COVID-19 a pandemic on March 11. It is the first pandemic caused by a coronavirus.

"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. We have therefore made the assessment that COVID-19 can be characterized as a pandemic," said Tedros Adhanom Ghebreyesus, director-general of the WHO.

"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. Describing the situation as a pandemic does not change WHO’s assessment of the threat posed by this virus. It doesn’t change what WHO is doing, and it doesn’t change what countries should do."

This image shows the new coronavirus in orange. The virus was isolated from a patient in the U.S. This image shows the new coronavirus in orange. The virus was isolated from a patient in the U.S. (Photo: NIAID-RML [CC BY 2.0]/Flickr)

Outside of mainland China, cases have been reported in nearly five dozen international locations. This real-time tracking map from Johns Hopkins University's Center for Systems Science and Engineering monitors confirms cases globally. (Be patient because sometimes data takes time to load.) The New York Times also has a map tracking the spread of the outbreak.

In late February, the virus spread in Europe and the Middle East. In Italy — which has the most cases of any country outside of Asia. Originally, authorities set up road blocks, called off soccer matches and closed some famed tourist sites like the famed La Scala opera house. But when cases began to multiply, eventually the entire country was put under lockdown.

There are at least 1,200 cases of the virus in the U.S. — including 49 cases among people repatriated from China and from the Diamond Princess cruise ship — according to the CDC. There have been 37 deaths.

The main symptom is fever, according to WHO, with some patients reporting difficulty breathing and cough and X-rays showing some lung lesions.

How fast is it spreading?

A woman wearing a protective mask rides a motorized bike on an empty road in Wuhan, China. A woman wearing a protective mask rides a motorized bike on an empty road in Wuhan, China. (Photo: Getty Images)

Health officials say the virus is thought to spread mainly from person to person. It may also be possible that a person can catch the virus by touching a surface that has the virus on it, then touching their mouth or nose.

People are thought to be the most contagious when they are the sickest and have the most symptoms, says the CDC. There are some reports that people can spread the virus before they have symptoms, but it's not believed to be the main way COVID-19 spreads.

Sixteen makeshift hospitals were built in Wuhan for patients infected with the virus. They were opened by the first week of February. The facilities were modeled after a hospital built in six days in Xiaotangshan for SARS patients, reports the Associated Press. The last of the hospitals closed by March 1 after it had already discharged its last patient, according to Reuters.

At least three separate research teams are working to develop potential vaccines against the virus, according to the Coalition for Epidemic Preparedness Innovations (CEPI). U.S. biotech firm Modern says its vaccine, called mRNA-1273, has been sent to the National Institute of Allergy and Infectious Diseases (NIAID) for initial testing just six weeks after research started, CNN reports. Testing and the approval process will take at least a year.

How worried are people?

woman arriving airport with mask A woman arriving on an international flight to Los Angeles International Airport wears a mask on the first day of health screenings for coronavirus of travelers from Wuhan, China, in January 2020. (Photo: David McNew/Getty Images)

The outbreak originally hit during the Lunar New Year holiday. During this time, millions of people typically travel throughout the country and abroad. In an effort to contain the disease, the Chinese government extended the holiday into early February. When factories and companies began opening for business again, some required managers to bar workers who traveled near Wuhan recently; others required employees to have their temperatures taken regularly.

Around the world, airports have tightened screenings of travelers coming from hard-hit areas. Several airlines have cut the number of flights they are operating out of hard-hit countries or are canceling them completely. In late February, Carnival Corporation, the parent company of nine cruise lines including Princess Cruises, announced it has cancelled all of its ships to mainland China through mid-March.

Originally, the U.S. state department advised against all travel to China and Iran and told Americans to avoid all non-essential travel to Italy and South Korea. On March 11, President Trump announced a ban, cancelling travel for some people from 26 European countries to the U.S.

Many colleges and universities have cancelled classes and emptied dorms in favor of online learning. Some cities and states have banned large gatherings. The NBA cancelled games after two players tested positive. Concerts, parades, sporting events and festivals have all been cancelled around the country and the world.

Coronavirus and pollution levels

map of nitrogen dioxide, a noxious gas emitted by motor vehicles, power plants, and industrial facilities. Satellite image show concentrations of nitrogen dioxide over China. NASA says the drop in pollution is 'partly related' to the virus outbreak. (Photo: NASA)

Wuhan has shut down public transportation, canceling planes and trains, as well as temporarily suspending bus, subway and ferry service to attempt to curb the spread of the epidemic, The New York Times reports. Travel restrictions and partial lockdowns are also in place in at least 15 cities, affecting almost 60 million people, according to CNN.

Part of the Great Wall, Shanghai Disneyland and Beijing's Forbidden City and many other places have been closed indefinitely.

The drop in activity may have also impacted pollution, according to NASA. The satellite images above show levels of nitrogen dioxide, a noxious gas emitted by motor vehicles, power plants and industrial facilities. The maps show NO2 concentrations before and during the quarantine. NASA scientists say there is evidence this is at least "partly" related to the economic slowdown because of the virus.

Editor's note: This story has been updated with new information since it was published in January 2020.

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

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