We combed through dozens of new studies about the coronavirus. The research suggests a suite of overlooked symptoms and up to 8 times more cases than reported.

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

Medical staff wearing protective clothing work inside a ward that receives any person who may have been infected with coronavirus, at the Rajiv Ghandhi Government General hospital in Chennai, India, January 29, 2020.
P. Ravikumar/Reuters

Scientists are racing to learn more about a new coronavirus that has swept through China and spread across the globe.

The virus, which may have jumped from animals to people at a market in the city of Wuhan, has killed over 1,000 people and infected over 43,000.

The World Health Organization (WHO) considers the outbreak a global public-health emergency – a declaration that has only been used five times since it was created in 2005.

Scientists worldwide are publishing a wealth of studies about the coronavirus, both in peer-reviewed journals and on pre-print servers without peer review, since that process can take months, and this virus is spreading quickly.

Although it’s preliminary, here’s what published research has shown so far.

The new virus is the seventh known member of the coronavirus family, which also includes the viruses that cause the common cold and pneumonia.

The crown shape of this virus gives it the coronavirus name.
BSIP/UIG Via Getty Images

Other coronaviruses include severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).

Though it is spreading quickly, the Wuhan coronavirus so far seems less deadly than MERS and SARS.

Shayanne Gal/Business Insider

So far, the mortality rate for the Wuhan coronavirus is around 2% based on the number of reported patients thus far.

But experts think that rate will evolve, since countries are still in the early stages of reporting.

"What we're seeing now in terms of illness and deaths reflect people who started getting sick a week ago," David Weber, a professor of epidemiology at the University of North Carolina at Chapel Hill, told Business Insider. "My guess is things will change over time."

The new coronavirus appears to be more infectious than SARS. Studies looking at the number of people an average patient infects suggest it could range from one to five.

A staff member checks the temperature of a passenger entering a subway station in Beijing, China on January 28, 2020.
Reuters/Carlos Garcia Rawlins

Knowing how many people the average patient infects ⁠- a number called the R0 (pronounced R-naught) ⁠- is crucial to understanding how a virus spreads.

So far, studies vary widely on the R0 of the Wuhan coronavirus. Most land in a range similar to that of SARS, about two or three, including an estimate from the WHO. But some studies have placed the R0 much higher, closer to five or six.

One peer-reviewed study estimated that 75,815 people in Wuhan had likely been infected by January 25 — nearly eight times the number of reported cases worldwide at the time.

This aerial photo on January 24, 2020 shows excavators at the construction site of a new hospital being built to treat patients from a deadly virus outbreak in Wuhan.
STR/AFP via Getty Images

The study, published in medical journal The Lancet, estimated that infected people would pass the virus to two to three others, on average, meaning the infected population would double every 6.4 days.

The researchers even accounted for the quarantine China has imposed on Wuhan and surrounding cities.

"Other major Chinese cities are probably sustaining localized outbreaks," the study authors wrote. "Large cities overseas with close transport links to China could also become outbreak epicenters, unless substantial public-health interventions at both the population and personal levels are implemented immediately."

The virus likely spread far beyond quarantined cities before China cut off transportation, according to some studies.

A man crosses an empty highway road on February 3, 2020 in Wuhan.
Getty Images

On January 23, local officials quarantined Wuhan by shutting down all public transportation - including buses, metros, and ferries. Trains and airplanes coming into and out of the city were also shut down, and roadblocks were installed to keep taxis and private cars from exiting.

China has also imposed travel restrictions on at least 16 cities in the Hubei province.

But one paper, which is awaiting publication in the CDC journal Emerging Infectious Diseases, found a 99% chance that at least one person carried the virus to the major cities of Beijing, Guangzhou, Shenzhen, and Shanghai before Wuhan's quarantine.

The findings come from travel data analysis and disease modeling by researchers at the University of Texas at Austin and other institutions in Hong Kong, mainland China, and France.

The study also found that there was a 50% chance that someone carrying the virus had traveled to at least 128 cities in China before the quarantine began.

Mask-wearing passengers in Shanghai catch one of the final trains into Wuhan before a lockdown was imposed on January 23, 2020.
Hector Retamal/AFP via Getty Images

"Given that 98% of all trips during this period are taken by train or car, our analysis of air, rail and road travel data yields more granular risk estimates than possible with air passenger data alone," Lauren Ancel Meyers, a co-author of the paper who studies infectious disease, said in a press release.

Outside China, Bangkok, Thailand is more at risk than any other city as the virus spreads, according to an analysis by population-mapping experts.

That's because the researchers estimated that Bangkok would receive over 1 million air travelers from China's most affected cities over a three-month period, starting 15 days before the Lunar New Year. Those Chinese cities included Beijing, Guangzhou, Shanghai, and Chongqing.

Thailand has so far reported at least 32 cases of the virus.

After Bangkok, that analysis identified Hong Kong, Taipei, Sydney, New York, and London as other high-risk cities.

A map shows global cities receiving airline travelers from 18 high-risk cities in mainland China over a three-month period.

The most at-risk countries were Thailand and Japan. The US placed sixth in the researchers' ranking.

"It's vital that we understand patterns of population movement, both within China and globally, in order to assess how this new virus might spread domestically and internationally," Andrew Tatem, a professor at the University of Southampton and a study co-author, said in a press release.

It's unclear whether people who are infected can spread the coronavirus before they show symptoms.

In a letter published in The New England Journal of Medicine, 20 doctors and researchers described a case in which this happened. They wrote that an otherwise healthy, 33-year-old German man developed a sore throat, chills, a cough, and a fever a few days after meeting with a business partner from China in mid-January. Three days later, he felt better and went back to work.

It turned out that the German man had contracted the Wuhan virus from his business partner. When the 33-year-old went back to work with no symptoms, he infected at least two of his colleagues.

But another letter from Germany's public health agency claimed that the researchers hadn't spoken with the business partner from China. The agency said she had later told investigators she had symptoms while in Germany, according to the journal Science.

SARS and MERS don't spread when people don't have symptoms. But preliminary research shows that less serious coronaviruses might.

A study published in medRxiv without peer review looked at common coronaviruses, which cause nothing more than a cold, and found the viruses inside nasal passages of people who reported no symptoms.

"It's going to leak out as they're speaking and breathing and coughing and sneezing and wiping their nose," Jeffrey Shaman, the lead author of that study, told NPR. "Whether it's ... a sufficient quantity to make somebody else infectious, we can't discern that from what we've done."

The period of time during which people carrying the coronavirus show no symptoms, called the incubation period, seems to last 2 to 14 days.

That's the assumption that the US Centers for Disease Control and Prevention (CDC) has adopted, based on the incubation period of MERS.

It's also the reason the White House decided to temporarily bar foreigners from entering the US if they have been to China within the past 14 days. US citizens who have been to the Hubei province of China - where Wuhan is located - within the prior 14 days could be quarantined for up to two weeks upon their return.

These policies, which went into effect on February 2, are meant to prevent people from spreading the virus before they know they've been infected.

One analysis of over 1,099 patients found that some had incubation periods as long as 24 days. That study has not been peer-reviewed, though.

Customers wearing face masks shop inside a supermarket following an outbreak of the novel coronavirus in Wuhan

The study was published in the pre-print repository medRxiv. The researchers concluded that the new coronavirus "spreads rapidly by human-to-human transmission."

Though the coronavirus is a respiratory disease, some research suggests it might also affect the digestive system.

People wearing masks shop at a supermarket on the second day of the Chinese Lunar New Year, following the outbreak of a new coronavirus, in Wuhan, China, January 26, 2020.

One study, shared in the pre-publication repository biorXiv without peer review, comes from researchers at the Second Military Medical University in Shanghai. They detected an enzyme signature of the virus in cells from the small intestine and colon.

Researchers detected the coronavirus' RNA in a US patient's poop, according to a report published in the New England Journal of Medicine.

Dr. Susan Kline, spokesperson for the Infectious Diseases Society of America, told MedPage Today that other coronaviruses appear in poop as well. SARS traveled through a Hong Kong apartment's sewage system and infected other residents after one sick person had diarrhea.

Kline said some health authorities may be overlooking the illnesses' gastrointestinal symptoms, like nausea, vomiting, and diarrhea.

An exhibition center converted into a hospital in Wuhan on February 5, 2020.
STR/AFP/Getty Images

The first US patient to be diagnosed had diarrhea and reported abdominal discomfort the day after he arrived at the hospital. Patients in China and Vietnam have also had diarrhea, vomited, or reported nausea.

Kline said that although healthcare workers should not expect all patients to have gastrointestinal problems, including those symptoms in official guidelines could help catch more coronavirus cases early on.

"That would be helpful for clinicians to have, so they could at least consider that a patient with novel coronavirus might have vomiting or diarrhea," Kline said.

Ignoring those rarer symptoms could have deadly consequences, since they are sometimes the first indicators that a person is infected.

One peer-reviewed study, published Friday in the Journal of the American Medical Association, identified 14 patients who had diarrhea and nausea before they showed any signs of fever or respiratory symptoms. That was 10% of the study's 138-person sample size.

One of those patients was placed in a surgical ward because they only showed abdominal symptoms, so doctors didn't suspect the new coronavirus. That patient transmitted the virus to at least 10 healthcare workers and four other patients in the ward.

Many coronavirus patients develop pneumonia with a build-up of fluid in their lungs.

Junqiang Lei, Junfeng Li, Xun Li, and Xiaolong Qi

A study released in the journal Radiology included scans of the chest of a 33-year-old woman from a hospital in Lanzhou, China. The scans show white patches in the lower corner of her lungs, which indicate what radiologists call "ground glass opacity."

"If you zoom in on the image, it kind of looks like faint glass that has been ground up," Paras Lakhani, a radiologist at Thomas Jefferson University who was not involved in the study but examined the images, told Business Insider. "What it represents is fluid in the lung spaces."

But in a follow-up examination of 21 patients who displayed symptoms of the virus, the researchers identified three patients with normal CT scans.

"We can't rely on CT alone to fully exclude presence of the virus," Michael Chung, the study's lead author, said in a statement.

The new coronavirus seems to have originated in bats.

Genetic analysis of samples of the coronavirus, called 2019-nCoV or COVID-19, from nine patients revealed it to be closely related to two SARS-like coronaviruses that came from bats.

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

That study, published in the The Lancet, suggests that an animal sold at a market in Wuhan could have caught the virus from bats then passed it to humans.

One genetic assessment found that the new coronavirus is more genetically similar to SARS-like viruses in bats than to human SARS or MERS.

A greater horseshoe bat (Rhinolophus FerrumEquinum), a relative of the Rhinolophis sinicus bat species from China that was the origin of the SARS virus.
De Agostini/Getty

The peer-reviewed analysis compared three genomes from the new coronavirus to many human SARS genomes, MERS genomes, and genomes from SARS-like coronaviruses in bats. The new coronavirus was most similar to the bat samples.

One study suggested that the virus jumped from bats to snakes to humans, but other researchers said that's unlikely.

Snakes hang from a wooden cabinet marked with the Chinese characters "poisonous snake," at a snake soup shop ahead of the Spring Festival in Hong Kong.
Reuters/Bobby Yip

In a peer-reviewed study published January 22 in the Journal of Medical Virology, a group of researchers in China suggested that snakes were the most likely animals to have passed the virus to humans.

Several other scientists have voiced their disagreement, however.

"They have no evidence snakes can be infected by this new coronavirus and serve as a host for it," Paulo Eduardo Brandão, a virologist at the University of São Paulo who is investigating whether coronaviruses can infect snakes, told Nature. "There's no consistent evidence of coronaviruses in hosts other than mammals and Aves (birds)."

Virologist Cui Jie, who was on a team that identified SARS-related viruses in bats in 2017, said this strain from Wuhan is clearly a "mammalian virus."

"Nothing supports snakes being involved," David Robertson, a virologist at the University of Glasgow, told Nature.

One group of researchers suggested that bats may have passed the virus to pangolins, which then passed it to humans.

A man holds a pangolin at a wild animal rescue center in Cuc Phuong, outside Hanoi, Vietnam, September 12, 2016.

Researchers from South China Agricultural University in Guangdong suggested that the coronavirus' intermediate host might have been the pangolin, an endangered mammal.

According to China's Xinhua news agency, the researchers found that samples of coronaviruses taken from wild pangolins and from infected patients are 99% identical.

But this research has yet to be published or confirmed by other experts.

Other possible intermediaries include pigs and civets.

Another genetic study of the coronavirus found that it shares 80% of its genome with SARS — enough that research to develop SARS treatments and vaccines could be applicable here.

A microscopic view of the SARS coronavirus.

"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 who was not affiliated with the study, said in a press release.

He added: "This indicates that treatments and vaccines developed for SARS should work for the Wuhan virus."

Growing the virus in a lab could help identify the antibodies humans produce before they show symptoms, and possibly help develop a vaccine.

BSIP/UIG Via Getty Images

This video, courtesy of Dr. Julian Druce at the Victorian Infectious Diseases Reference Laboratory, shows the Wuhan coronavirus that Australian scientists grew from a patient sample at the Doherty Institute. It's the first time a lab outside China has grown the virus.

The lab-grown sample could help identify people who aren't yet showing symptoms but are still infected and capable of spreading the virus.

"An antibody test will enable us to retrospectively test suspected patients so we can gather a more accurate picture of how widespread the virus is, and consequently, among other things, the true mortality rate," Dr. Mike Catton, deputy director of the Peter Doherty Institute for Infection and Immunity, said in a statement. "It will also assist in the assessment of effectiveness of trial vaccines."

While some researchers are looking for a vaccine, others are developing treatments. Clinical trials are testing HIV medications against the new virus.

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

Medical staff with protective clothing work inside a ward specialised in receiving any person who may have been infected with coronavirus, at the Rajiv Ghandhi Government General hospital in Chennai, India, January 29, 2020.
P. Ravikumar/Reuters

Johnson & Johnson, AbbVie, and Gilead Sciences have all donated antiviral drugs to Chinese health authorities to run tests against the virus.

There are nine clinical trials testing various drugs, mainly antiviral therapies, against the coronavirus, BioCentury reported. Six of those studies are testing medicines approved to treat HIV, hepatitis B, or hepatitis C.

If effective, these drugs could be a short-term solution while companies race to develop vaccines. Those efforts will likely take longer because vaccines typically require multiple rounds of clinical testing that can span several years.

The first US patient received an experimental drug called remdesivir.

Employees dressed in scrubs talk with each other at Providence Regional Medical Center after coronavirus victim treated in Everett, Washington.

The treatment appeared effective, though the researchers who reported the case said more robust testing is needed. Remdesivir was initially developed to fight Ebola.

Gilead, the biotech company that developed remdesivir, has donated enough of the drug for 500 patients to Chinese health officials. The company is working with local hospitals to run tests, Merdad Parsey, Gilead's chief medical officer, told Bloomberg on Tuesday.

"Beyond all, this global health threat teaches, once again, that it is far better to invest in preparedness to prevent, rapidly identify, and contain outbreaks at their source," Georgetown University researchers wrote.

A member of the Thai Airways crew disinfects the cabin of an aircraft of the national carrier during a procedure to prevent the spread of the coronavirus at Bangkok's Suvarnabhumi International Airport, Thailand, January 28, 2020.
Athit Perawongmetha/Reuters

In their analysis of government responses to the virus, published January 30 in the Journal of the American Medical Association, they added: "Reacting after a novel infection has spread widely (perhaps overreacting with travel bans and quarantines) costs lives, economic resources, and the well-being of millions of people currently cordoned off in a zone of contagion."

Correction: A previous version of this post used a chart with inaccurate data about the 2009 H1N1 outbreak. It has been removed.