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A coronavirus that originated in Wuhan, China has killed nearly three times as many people in eight weeks than severe acute respiratory syndrome (SARS) did in eight months.

More than 2,100 people have died from the Wuhan coronavirus, and at least 75,500 have been infected across 27 countries. (For the latest case total, death toll, and travel information, see Business Insider's live updates here.)

The new disease, called COVID-19, is marked by fevers and pneumonia-like symptoms. It's conjured a sense of déja vu for some who remember the SARS outbreak that started in November 2002. SARS was also a coronavirus, and it jumped to people from animals in wet markets, which the new coronavirus probably did, too. The two viruses share 80% of their genetic codes.

Experts called SARS "the first pandemic of the 21st century," since it spread across 29 countries. The virus emerged in Guangdong and infected 8,098 people over the course of eight months, killing 774. Just a month after the first confirmed case of the novel coronavirus, the total global case count surpassed that of SARS.

The new coronavirus appears to be less deadly than SARS, however. The mortality rate for SARS was 9.6%, whereas COVID-19 seems to kill between 1% and 2% of those infected.

"In essence, it's a version of SARS that spreads more easily but causes less damage," Ian Jones, a virologist at the University of Reading in the UK, said on February 3.

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Here are some of the crucial differences between this outbreak and the SARS pandemic 17 years ago.

The first report of the novel coronavirus came on December 31, though some people might have gotten sick earlier that month.

Wuhan

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Wuhan is a city of 11 million people in the central province of Hubei, China. SARS originated in the Guangdong province in southeastern China, near Hong Kong.

Patients with SARS experienced fevers, headaches, and a type of deadly pneumonia that could cause respiratory failure. That virus hasn't been seen in humans since July 2003.

The new coronavirus has spread far faster than SARS did.

FILE PHOTO: A nurse wearing protective gear walks outside a Severe Acute Respiratory Syndrome Clinic (SARS) in suburban Toronto, April 24, 2003. REUTERS/Mike Cassese/File Photo

Reuters

It took eight months for SARS to infect more than 8,000 people. COVID-19 has infected more than 75,000 people in about eight weeks.

Most experts think the new coronavirus' incubation period ranges from one to 14 days, though a recent study from China's National Health Commission (which has yet to be peer-reviewed) suggested it could be as long as 24 days. SARS' average incubation period, by comparison, was seven days.

The new coronavirus may jump between people before patients show symptoms, but scientists aren't sure about that yet, either.

The new coronavirus' fatality rate has not yet been determined with accuracy, but it seems to be between 1% and 2.3% so far. The SARS fatality rate was 9.6%.

In this Friday, Jan. 24, 2020, photo released by China's Xinhua News Agency, a medical worker attends to a patient in the intensive care unit at Zhongnan Hospital of Wuhan University in Wuhan in central China's Hubei Province. China expanded its lockdown against the deadly new virus to an unprecedented 36 million people and rushed to build a prefabricated, 1,000-bed hospital for victims Friday as the outbreak cast a pall over Lunar New Year, the country's biggest, most festive holiday. (Xiong Qi/Xinhua via AP)

Associated Press

A study from the Chinese National Health Commission looked at 1,099 coronavirus cases and found the fatality rate to be 1.4%. A February 10 report from the World Health Organization (WHO) suggested that this rate could be even lower: about 1%.

However, the biggest study to date revealed a 2.3% fatality rate among 72,000 patients. And research published in The Lancet found that the fatality rate among a group of 99 coronavirus patients studied was about 11%.

One month into SARS outbreak, only five people had died. The new coronavirus had killed at least 213 people by that mark. The COVID-19 death toll surpassed that of SARS on February 8.

Researchers have found similarities between lung scans of SARS patients and those with the new coronavirus.

sars x-rays

Agence France Presse

In a study released January 31, a group of researchers at Lanzhou University analyzed two CT scans of a 33-year-old coronavirus patient's lungs.

Paras Lakhani, a radiologist at Thomas Jefferson University who was not involved in the study but examined the images, told Business Insider that the scans had "a lot of similar features," to those of SARS patients' lungs.

"If you zoom in on the image, it kind of looks like faint glass that has been ground up," he said. "What it represents is fluid in the lung spaces."

The study authors noticed that those ground-glass patches extend to the edges of the patient's lungs.

"That's something we don't often see," Lakhani said. "We saw that with severe acute respiratory syndrome (SARS) and we saw that with Middle East respiratory syndrome (MERS)." MERS is another type of coronavirus found in people.

The genetic sequence of the new coronavirus is 79.5% similar to that of SARS.

FILE - In this Wednesday, Jan. 22, 2020, file photo, a staff member moves bio-waste containers past the entrance of the Wuhan Medical Treatment Center in Wuhan, China, where some people infected with a new virus are being treated. The new virus comes from a large family of coronaviruses, some causing nothing worse than a cold. Others named SARS and MERS have killed hundreds in separate outbreaks. (AP Photo/Dake Kang, File)

Dake Kang/AP

Both SARS and the new coronavirus belong to a particular virus lineage called betacoronaviruses, which can make the jump to humans and nest in our respiratory tracts.

SARS and the new coronavirus both dock to the same human cell receptor, called ACE2, deep in people's lungs.

FILE - This illustration provided by the Centers for Disease Control and Prevention (CDC) in January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). Health officials hope to avoid stigma and error in naming the virus causing an international outbreak of respiratory illnesses. But some researchers say the current moniker, 2019 nCoV, which stands for 2019 novel coronavirus, probably won't stick in the public's mind. (CDC via AP, File)

Associated Press

That may explain patients' pneumonia-like symptoms.

In general, a coronavirus' circular shell is peppered with spike-shaped proteins that help it attach to a host's cell. If the spikes don't fit receptors on a potential host's cells, the virus can't spill over. But when a coronavirus mutates, the shape of these proteins gets altered, and that sometimes allows the virus to dock in a new host.

A new study that looked at the 3D molecular structure of these spike-shaped proteins found that the bonds between the new coronavirus' proteins and human receptors is 10 times higher than we saw with SARS.

coronavirus protein 3D model

Jason McLellan/University of Texas at Austin

This finding could explain why COVID-19 is so much more contagious than SARS and more easily jumps from person to person.

Genetic studies also help experts pinpoint which animal passed the coronavirus to people. This new virus is nearly identical to other coronaviruses circulating in Chinese bat populations — 96% of the genetic codes match.

horseshoe bat

De Agostini/Getty

Coronaviruses are zoonotic diseases (meaning they can jump from animals to people).

Bats were the original hosts of SARS, too; the animals can pass diseases to other species via their poop or saliva, and the unwitting intermediaries can transmit those viruses to humans.

"Bats and birds are considered reservoir species for viruses with pandemic potential," Bart Haagmans, a virologist at the Erasmus Medical Center in Rotterdam, Netherlands, told Business Insider.

Many experts think the new coronavirus jumped to humans at the Huanan Seafood Wholesale Market in Wuhan.

SARS jumped from bats to weasel-like mammals called masked palm civets, then to humans. The spillover happened in wet markets in Guangdong, China.

civet

Oleksandr Rupeta/NurPhoto/Getty

Researchers traced SARS to a population of horseshoe bats in China's Yunnan province. These bats lived in a cave just 1.1 kilometer from the nearest village.

The most likely intermediary species for the new coronavirus are bats, pigs, civets, or pangolins (not snakes, as some researchers initially suggested). That's because these animals also have the same ACE2 receptors.

According to the World Health Organization (WHO), 50% of people impacted by SARS were age 65 or older, while the other half of infected patients varied widely in age.

sars

PETER PARKS/AFP via Getty Images

A study of 17 patients who died from coronavirus complications reported that their median age was around 75. Many had other health issues like high blood pressure, diabetes, and Parkinson's disease.

Other studies have estimated the average ages of infected patients to be between 47 and 55. The Chinese study of 72,000 cases revealed that more than 75% of patients were between 30 and 69.

Chinese researchers in Hong Kong estimated that one person with the coronavirus can pass it to three to five others — a statistic called the virus' R0 value.

Health Officials in hazmat suits wait at the gate to check body temperatures of passengers arriving from the city of Wuhan Wednesday, Jan. 22, 2020, at the airport in Beijing, China. Nearly two decades after the disastrously-handled SARS epidemic, China’s more-open response to a new virus signals its growing confidence and a greater awareness of the pitfalls of censorship, even while the government is as authoritarian as ever. (AP Photo Emily Wang)

Emily Wang/AP

That study has not yet been peer-reviewed, however, and WHO researchers estimate the coronavirus' R0 value to be lower: between 1.4 and 2.5 people.

The WHO declared the coronavirus a public-health emergency of international concern on January 30. SARS did not get the same designation because the WHO has only used it since 2005.

lunar new year hong kong china masks wuhan coronavirus

Passengers wear protective face masks at the departure hall of the high-speed train station in Hong Kong, January 23, 2020.

AP Photo/Kin Cheung

It has been used five other times.

Chinese authorities initially attempted to hide the SARS outbreak from the WHO. But Liu Heng, an adviser to China's cabinet, told Reuters that China announced the new outbreak much more immediately.

Sars

AHMAD YUSNI / AFP) (Photo by AHMAD YUSNI/AFP via Getty Images

The Chinese government didn't inform the WHO about SARS until February 14, 2003 — 88 days after the first reported case. According to The Sydney Morning Herald, doctors in Beijing were ordered by authorities to hide SARS patients from WHO officials during inspections.

During the initial stages of that outbreak, the Chinese government also concealed information from the public, which exacerbated the spread of disease.

"We are doing much better now ... We are paying greater attention to preventing the epidemic," Liu said on January 22.

In this Tuesday, Jan. 21, 2020, photo, a worker monitors display screens for infrared thermometers as they check travelers at Hankou Railway Station in Wuhan in southern China's Hubei province. The U.S. on Tuesday reported its first case of a new and potentially deadly virus circulating in China, saying a Washington state resident who returned last week from the outbreak's epicenter was hospitalized near Seattle. (Chinatopix via AP)

Associated Press

Still, at least five people in China have disappeared, gotten arrested, or been silenced after speaking out about the coronavirus.

Chinese public-health experts quickly shared the new coronavirus' genetic information with researchers around the globe. It took four months for the SARS genome to be published.

Coronavirus mask Wuhan China

Getty Images

"The speed with which this virus has been identified is a testament to changes in public health in China since SARS and strong global coordination through the WHO," Jeremy Farrar, an infectious-diseases specialist who studied SARS, told Reuters.

Chinese authorities also quickly instituted travel lock-downs this time. During the SARS outbreak, it took officials at least four months to institute quarantine measures.

A policeman uses a digital thermometer to take a driver's temperature at a checkpoint at a highway toll gate in Wuhan in central China's Hubei Province, Thursday, Jan. 23, 2020. China closed off a city of more than 11 million people Thursday in an unprecedented effort to try to contain a deadly new viral illness that has sickened hundreds and spread to other cities and countries amid the Lunar New Year travel rush. (Chinatopix via AP)

Chinatopix/AP

Authorities quarantined Wuhan on January 23, halting all public transportation, including city buses, trains, and ferries. The order prevents any buses or trains from coming into or leaving the city and grounds all planes at the Wuhan airport.

By January 27, 15 additional cities had followed suit with their own travel restrictions.

The lockdown restrictions affect at least 50 million people in China's Hubei province, where Wuhan is located.

Wuhan virus China Beijing railway station

Kevin Frayer/Getty Images

Another 100 million people in China are subject to restrictions on how often they can leave their homes, according to The New York Times.

Neither SARS nor the Wuhan coronavirus has a vaccine.

FILE PHOTO: A nurse fills a syringe with a vaccine before administering an injection at a children's clinic in Kiev, Ukraine August 14, 2019. REUTERS/Valentyn Ogirenko

Reuters

Five leading drug companies — Johnson & Johnson, Regeneron Pharmaceuticals, GlaxoSmithKline, Moderna, and Gilead Sciences — have announced plans to research and develop treatments for the new virus.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on February 7 that the agency is collaborating with Moderna to develop a coronavirus vaccine.

As long as there aren't any glitches, Fauci said, "we will be in people in a phase-one trial within the next 2.5 months."

But getting a vaccine to market has historically been an arduous, multi-year process (the Ebola vaccine took 20 years to make).

"A vaccine best-case scenario is three-quarters of a year, if not longer," Vincent Munster, a virologist at the Rocky Mountain Laboratories, told Business Insider.

Some researchers are also testing existing drugs as treatment options.

There is one benefit to the genetic similarity between SARS and the new coronavirus: Work to develop treatments for the former might be applicable for the latter.

wuhan coronavirus medical staff india hospital

Medical staff with protective clothing work inside a ward specialized in receiving any person who may have the coronavirus, at the Rajiv Ghandhi Government General hospital in Chennai, India, January 29, 2020.

P. Ravikumar/Reuters

Because SARS and the new coronavirus bind to human cells in the same way, research that's already been done about the former could provide a head-start for the latter.

Rosie Perper and Aria Bendix contributed reporting to this story.

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