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There are so many unknowns about the novel coronavirus that has triggered unprecedented quarantine efforts, dangerous conspiracy theories and global alarm. Much of what we know about coronaviruses comes from the ones that we’ve dealt with before — ranging from deadly global health threats such as severe acute respiratory syndrome (SARS) to versions that cause the common cold. New information is coming in on a daily basis, but here’s what we know so far about the respiratory virus that has, as of Feb 16, infected more than 69,000 people and killed more than 1,600 people, all but four on the Chinese mainland.

How deadly is the new coronavirus?

The good news is that public health officials say the new coronavirus is less deadly than SARS, which killed about 10 percent of people who were infected during the outbreak that began in 2002. But an urgent question needs to be answered as soon as possible: How much less deadly is it? About 2 percent of the reported cases as of Feb. 7 have been fatal, but many experts say the death rate could be lower. That’s because early in an outbreak, mild illnesses may not be reported. If only people with severe illness — who are more likely to die — seek care and are confirmed as being sick, the virus will appear much more deadly than it really is, because of all the uncounted people with milder symptoms.

“The first question is: What is the true burden of infection? We don’t understand the true burden of mild illness,” said Amesh Adalja, an infectious-disease expert at the Johns Hopkins Center for Health Security. “How much is this spreading in the community, unbeknown to everybody, mixed in with flu and cold?”

Early in the outbreak, one expert estimated that although 2,000 cases had been reported, 100,000 were probably already sick.

Understanding how deadly the disease is and how many people really have it matters crucially to developing a public health response and preparing hospitals and the health-care system around the world.

How easily does it spread?

The bad news is that the new coronavirus appears to spread much more easily than SARS and instead is similar to other coronaviruses that cause cold-like symptoms, Adalja said.

A virus that can spread fairly easily — and may already be fairly widespread — presents a huge public health challenge.

“To complicate things even more, we don’t know which individuals are likely to spread the virus,” said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine. “Is it those with more serious respiratory infections or coughing, or are those who have mild symptoms equally likely to be spreading it? I think we don’t know that at this point.”

A case report that showed the illness could spread before symptoms occurred turned out to be incorrect, although a top U.S. official has said he still believes it can spread without symptoms, based on discussions with Chinese experts. Figuring out exactly how easily it spreads and who is infectious will be necessary for designing public health measures that are more likely to work.

“In SARS, which is often cited as the other example, it seemed people were quite sick before they started transmitting, and that’s why, in my view, SARS was ultimately controlled,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health. “You really could isolate the discernibly sick people.”

Who is most at risk of severe illness?

So far, the risk factors for developing severe illness are thought to be similar to those for other respiratory illnesses. Older people and those with underlying illnesses, such as diabetes or high blood pressure, are at increased risk. Early studies have also suggested men are at greater risk.

But there can be tremendous individual variation in how people respond — as with other diseases. For example, most 17-year-olds will get better from the flu after a miserable week or two. But occasionally, a healthy 17-year-old will die. Some people with a strep infection will develop a sore throat, but an unlucky few will develop a flesh-eating infection that can kill them. The same thing will happen with this virus — there will be people with known risk factors who recover, as well as people who develop severe cases for reasons we don’t understand.

“It may be a very specific thing about the way your immune system interacts with a particular pathogen,” said Allison McGeer, an infectious-disease epidemiologist at the University of Toronto. “It may also be just about exactly what your exposure is, something specific to what happened to you on that day, with that pathogen.”

Figuring out who is most vulnerable will be essential to designing preventive measures, such as prioritizing who gets a vaccine if one is developed.

What happens next?

An optimistic scenario is that the virus is contained in China and there isn’t any significant person-to-person transmission in other countries. This is looking increasingly unlikely to some experts.

“Many of the drastic actions in China — going door-to-door [doing temperature checks], quarantine of 50 million people, draconian measures that seem to be out of a Hollywood movie — they are premised on the fact that this is still containable,” Adalja said. “The evidence points to the fact that it is not containable.”

If the virus takes hold outside China, the biggest threat is not thought to be to countries such as the United States or others with well-resourced health-care systems.

“The numbers will go up in the U.K., U.S., Western Europe, but there seems to be enough warning in advance to potentially halt this epidemic in the U.S. and in Europe. Numbers will go up, but it shouldn’t look anything near like what we’re seeing in China,” Hotez said. “I can’t guarantee that, but the countries I’m more worried about are where there’s a lot of transportation back and forth with China and depleted health systems.”

How do you treat this coronavirus illness?

There is no specific antiviral treatment recommended for this infection. People who have gotten sick should receive supportive care to help relieve symptoms.

World Health Organization (WHO) expert Mike Ryan said he expected “that recovered patients would be protected from a further infection,” but that it remained unclear how long the immunity would last and if it would apply to other coronaviruses as well.

How do you protect yourself from getting infected?

There is currently no vaccine to prevent infection. The best way to protect yourself is to use the same common-sense actions experts recommend for preventing the spread of other respiratory viruses, such as flu and cold. Stay away from people who are sick. Wash your hands often with soap and water for at least 20 seconds, especially after going to the bathroom, before eating and after blowing your nose, coughing or sneezing.

If you don’t have access to soap and water, use an alcohol-based hand sanitizer with at least 60 percent alcohol. Avoid touching your eyes, nose and mouth with unwashed hands.

Stay home when you are sick. Cover your cough or sneeze with a tissue and throw the tissue in the trash. Or sneeze like a vampire, into your elbow rather than your hand.

Clean and disinfect frequently touched objects and surfaces using a regular household cleaning spray or wipe.

Why are there two new names for the coronavirus epidemic?

There are two new names associated with the unfolding epidemic: The “novel coronavirus” has been designated “severe acute respiratory syndrome coronavirus 2,” or more simply “SARS-CoV-2.” The disease it causes is “covid-19.”

The name of the disease was announced by the director general of the World Health Organization on Feb. 11. The naming of the virus came from a committee of experts who published a paper on a biology preprint site that described their research and rationale for giving the new virus a derivative name.

“It will be like HIV and AIDS — different names for virus and disease,” said Benjamin Neuman, a virologist at Texas A&M University at Texarkana and a co-author of the paper.

The naming of the virus came after close study of its genetic makeup by a dozen scientists, including Neuman, who form the Coronavirus Study Group, part of the International Committee on Taxonomy of Viruses.

Neuman said the new virus is the same species as the virus that caused the outbreak of Severe Acute Respiratory Syndrome (SARS) in China in 2002-2003.

“Same species, but different member of the species,” Neuman said.

WHO Director General Tedros Adhanom Ghebreyesus explained some of the process behind the illness’ naming.

“We had to find a name that did not refer to a geographical location, an animal, an individual or group of people, and which is also pronounceable and related to the disease,” he said, citing WHO guidelines adopted in 2015.

Covid-19 is a combination of coronavirus, disease and the year the pathogen was first identified, the WHO explained. The name also allows for future coronavirus diseases to be named following this formula, with the year of any new outbreak replacing 19.

Why did China revise its numbers for Hubei province?

On Feb. 13, China’s National Health Commission revised its case numbers for Hubei province, the center of the outbreak, far higher to reflect coronavirus diagnoses made by doctors’ clinical assessments rather than the results of nucleic acid testing kits.

Chinese experts have argued that the testing kits, which sample mucus swabbed from the upper respiratory tract, are both inaccurate and lacking in supply, and therefore do not reflect the true number of infections and deaths from the coronavirus.

Commission spokesman Mi Feng Mi told reporters that Hubei province changed its diagnosis criteria from every other region so that its patients could receive the appropriate care sooner and more efficiently. So far, jurisdictions beyond Hubei have not switched to the different diagnosis guidelines.

Isaac Bogoch, an infectious disease specialist at Toronto General Hospital, cautioned that the uptick is probably a reflection of what many public health experts knew all along — that China’s initial data vastly underestimated the breadth of the outbreak from the beginning.

“People who have been following this closely knew that this was much bigger than the reported numbers,” Bogoch said. “We knew we were dealing with a health-care system that was exceeding its capacity, and I don’t think this comes to anyone’s surprise.”

China’s health system is overburdened. Patients are seeking treatment wherever they can find a bed — which sometimes means in makeshift clinics in converted gymnasiums and conference centers.

“One of the problems with using lab-confirmed cases to monitor the spread of [an] epidemic is if there’s a ceiling in the number of tests that can be processed,” said Benjamin Cowling of the School of Public Health at Hong Kong University. “We’ve always known there were more coronavirus infections than the confirmed number of cases. It’s a very sensible move.”

Mike Ryan, executive director of the WHO’s Health Emergencies Program, said the spike in cases “does not represent a significant change in the trajectory of the outbreak,” though he cautioned that they still don’t know “how big that iceberg is.”

What do reports of a patient being ‘cured’ mean?

There are two kinds of “cured” in an infectious disease context, said Bruce Ribner, a professor at the Emory University School of Medicine.

There’s being “clinically cured,” he said, when someone starts feeling better and stops showing symptoms such as fever and coughing. Then there’s being “pathogen cured,” when doctors determine that the virus is indeed no longer in the body and therefore the patient can’t transmit the disease.

The former is clear to a patient. The latter, “we don’t yet have a good handle on what it takes,” said Ribner.

Scientists are busy trying to find out as much as they can about the coronavirus, including how long the transmission period lasts. As part of that process, they’ll also learn more about how to define “cured” in both senses.

There still remains no antiviral available to treat the novel coronavirus. But Todd Ellerin, director of infectious diseases at South Shore Health in Massachusetts, said that, as with the influenza, “most patients are cured of this on their own” just by their immune system fighting back against the invading virus. For others, especially older people and those with preexisting illness, the novel coronavirus infection can be far more severe and deadly.

Lauren Sauer, an assistant professor of emergency medicine at Johns Hopkins University, said that people with the virus should expect long hospital stays.

“We don’t have a definition of what cured is,” she said. “We don’t really have a good understanding of what [definition] people are using globally.”

In Hubei province, Sauer said, authorities “are being overly cautious” given the uncertainty over how long someone remains contagious. There, she said, a patient is considered cured when they haven’t had a fever for three days and have tested negative twice on a PCR test, which looks for the virus in the body.

When will it end?

This coronavirus could follow a seasonal pattern, peaking in the winter months. It could infect lots of people now and then begin to recede in the Northern Hemisphere before returning in the fall. It could take hold in the Southern Hemisphere.

“This virus can do anything it wants,” McGeer said. “That pattern of how it’s going to spread is completely unknown, but it is critical to what the burden is going to be to all of us. … It could be just like another coronavirus, a bunch of colds. It could be like a regular flu season. It’s possible it could be different and worse.”

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