What We Know About the Coronavirus, From Symptoms to Who Is at Risk

Health officials are worried about a growing number of cases outside China

Passengers wearing protective face masks at a train station in Hong Kong.

Photo: Kin Cheung/Associated Press

Scientists and public-health officials are learning more about the new coronavirus behind an epidemic that has reached dozens of countries. We are updating our questions and answers regularly to keep up with their findings. Here is what they know so far, and how you can minimize your risk.

The Latest on the Coronavirus

  • China says 39,002 people have been cured of the virus and discharged, exceeding the more than 37,000 people who are still infected
  • South Korea reports 800 new coronavirus cases; total rises to 3,150 with four dead
  • U.S. Food and Drug Administration to allow labs to begin testing for coronavirus; California, Oregon and Washington report three new cases with no travel history to China
  • Confirmed cases in Iran jumped more than 50% overnight to 593
  • Italy reports it has 888 coronavirus cases and 21 people have died
What is a coronavirus?

This virus belongs to a family of viruses28365365体育投注 known as coronaviruses. Named for the crown-like spikes on their surfaces, they infect mostly bats, pigs and small mammals. But they mutate easily and can jump from animals to humans, and from one human to another. In recent years, they have become a growing player in infectious-disease outbreaks world-wide.

Seven strains are known to infect humans, including this new virus, causing illnesses in the respiratory tract. Four of those strains cause common colds. Two others, by contrast, rank among the deadliest of human infections: severe acute respiratory syndrome, or SARS, and Middle East respiratory syndrome, or MERS.

28365365体育投注This new virus is called severe acute respiratory syndrome coronavirus 2, or Sars-CoV-2. The disease it causes is called Covid-19. (The number stands for 2019, the year it emerged.)

What are the symptoms of the illness and how do you know if you have it?

The virus infects the lower respiratory tract. Patients initially develop a fever, cough and aches, and can progress to shortness of breath and complications from pneumonia, according to case reports. They might develop nausea, with vomiting and diarrhea. Some become only mildly ill, or are infected but don’t get sick. Others are mildly ill for a few days, then rapidly develop more severe symptoms of pneumonia.

Some patients haven’t had a fever initially or might develop a “walking pneumonia,” meaning they might spread their infection to others because they aren’t sick enough to be in a hospital.

Epidemic Potential

Coronaviruses are jumping increasingly from animals to humans, creating new threats

NL63 (1100s)

SARS (2003)

229E (1800s)

MERS (2012)

OC43 (1800s)

Wuhan CoV (2020)

HKU1 (unknown)

Source: Timothy Sheahan, University of North Carolina

How deadly is it?

The mortality rate has ranged between 2% and about 3.4%, according to calculations of confirmed cases and deaths world-wide, which change daily. But the true rate won’t be known until epidemiologists can determine the denominator, meaning how many people have actually been infected. That number will include people who never had symptoms, or had a flulike illness but never got a test for Covid-19.

28365365体育投注Covid-19 appears to be less deadly than a related pathogen—SARS, which erupted in China in 2002 and spread globally in 2003. SARS killed about 10% of the people it infected. It is less deadly than MERS or Ebola.

28365365体育投注But this new virus spreads from one person to another more easily than SARS, some disease modeling and case studies suggest.

Who is most at risk?

28365365体育投注Adults of all ages have been infected, but the risk is highest for older people and those with other health conditions such as diabetes. Most of the 1,023 people whose deaths were included in a study by the Chinese Center for Disease Control and Prevention were age 60 or older, and/or had other illnesses. Many patients who have died were admitted to hospitals when their illness was advanced. One large study in China found a mortality rate of 14.8% in people ages 80 and older, and 8% in people ages 70 to 79, compared with a 2.3% mortality rate overall in the population studied.

Few children have been reported with the infection, but that could change.

How at risk is someone in the U.S.?

The current risk to the U.S. public is low, says the U.S. Centers for Disease Control and Prevention. The virus isn’t spreading widely. Most people who have been confirmed with the illness were infected while abroad and quarantined upon their return to the U.S. But the number of nontravel-related cases is growing, and the agency says it expects the virus to spread more widely in the country. It is preparing for that likelihood and urging people to take precautions.

Coronaviruses: From Animals to Humans

Researchers aren't sure how the novel coronavirus first infected people in China, but the viruses that cause SARS and MERS, which originated in bats, provide clues.

2

1

28365365体育投注Proteins on the outer shell of the virus allow it to latch onto cells in the host’s respiratory tract. The proteins’ shapes are determined by the virus’s genes.

To infect new hosts, the virus’s genes undergo mutations that alter its surface proteins, allowing them to latch onto the cells of new species.

Bat respiratory tract

28365365体育投注Human respiratory tract

Cell

Virus

Gene

Protein

Mutation

3

In the case of SARS, the virus jumped from bats to civet cats before gaining the ability to infect humans. In the case of MERS, camels served as the intermediate host.

Original host

28365365体育投注Intermediate host

Human

4

28365365体育投注Coronaviruses can also jump directly to humans, without mutating or passing through an intermediate species.

5

Researchers have found the novel coronavirus likely originated in bats, but haven't pinpointed the source of transmission to humans.

2

1

28365365体育投注Proteins on the outer shell of the virus allow it to latch onto cells in the host’s respiratory tract. The proteins’ shapes are determined by the virus’s genes.

28365365体育投注To infect new hosts, the virus’s genes undergo mutations that alter its surface proteins, allowing them to latch onto the cells of new species.

Bat respiratory tract

28365365体育投注Human respiratory tract

Cell

Virus

Gene

Protein

Mutation

3

28365365体育投注In the case of SARS, the virus jumped from bats to civet cats before gaining the ability to infect humans. In the case of MERS, camels served as the intermediate host.

28365365体育投注Original host

28365365体育投注Intermediate host

Human

4

28365365体育投注Coronaviruses can also jump directly to humans, without mutating or passing through an intermediate species.

5

28365365体育投注Researchers have found the novel coronavirus likely originated in bats, but haven't pinpointed the source of transmission to humans.

2

1

Proteins on the outer shell of the virus allow it to latch onto cells in the host’s respiratory tract. The proteins’ shapes are determined by the virus’s genes.

28365365体育投注To infect new hosts, the virus’s genes undergo mutations that alter its surface proteins, allowing them to latch onto the cells of new species.

Bat respiratory tract

Human respiratory tract

Cell

Virus

Gene

Protein

Mutation

3

In the case of SARS, the virus jumped from bats to civet cats before gaining the ability to infect humans. In the case of MERS, camels served as the intermediate host.

Original host

Intermediate host

Human

4

Coronaviruses can also jump directly to humans, without mutating or passing through an intermediate species.

5

28365365体育投注Researchers have found the novel coronavirus likely originated in bats, but haven't pinpointed the source of transmission to humans.

1

Proteins on the outer shell of the virus allow it to latch onto cells in the host’s respiratory tract. The proteins’ shapes are determined by the virus’s genes.

Bat respiratory tract

Cell

Virus

Gene

Protein

2

To infect new hosts, the virus’s genes undergo mutations that alter its surface proteins, allowing them to latch onto the cells of new species.

Mutation

28365365体育投注Human respiratory tract

3

28365365体育投注In the case of SARS, the virus jumped from bats to civet cats before gaining the ability to infect humans. In the case of MERS, camels served as the intermediate host.

Original host

28365365体育投注Intermediate host

4

Human

4

Coronaviruses can also jump directly to humans, without mutating or passing through an intermediate species.

5

Researchers have found the novel coronavirus likely originated in bats, but haven't pinpointed the source of transmission to humans.

Source: Timothy Sheahan, University of North Carolina

Alberto Cervantes and Josh Ulick /THE WALL STREET JOURNAL

How is the virus spread among humans?

28365365体育投注It transmits through “respiratory droplets” when an infected person speaks, coughs or sneezes, according to the World Health Organization. The droplets spread through the air and can land on another person’s mouth or nose, or possibly be inhaled into their lungs, infecting them. The droplets can also settle on nearby surfaces, where they can survive for a period, though it isn’t known how long. A person can become infected by touching a contaminated surface, then touching their mouth, nose or eyes.

Respiratory droplets are heavy and don’t travel far in the air, so transmission is believed to occur mostly through close contact, meaning within 6 feet of an infected person.

28365365体育投注Scientists are also investigating whether the new coronavirus might spread through urine or feces. Tests have found it in the digestive tract of some patients.

How easily does it spread?

28365365体育投注Disease-modeling experts have estimated that on average, each infected person has transmitted the virus to about 2.6 others, though the range is between 1.5 and 3.5. Those rates are higher than for some influenza viruses, some are lower than SARS, and they are far lower than measles, in which one infected person can transmit the virus to 12 to 18 other people.

28365365体育投注Public-health experts caution that these estimates are preliminary, change over time and can be lowered by measures to prevent the virus from spreading.

What is the incubation period?

People become ill between two and 14 days after infection, according to most estimates. One report described a person who became ill 27 days after infection. However, Chinese researchers recently cited an average incubation period of 5.2 days.

Is there a test?

Yes, there are diagnostic tests, which are the only way to confirm for certain whether a patient has the coronavirus or another infection. Because symptoms of Covid-19 are like those of the flu, the tests are given only to people who doctors or public-health officials believe might have the disease. In the U.S., the tests are conducted by public-health laboratories. In Hubei province, China, cases have also been diagnosed based on chest X-rays and symptoms.

28365365体育投注A blood test was recently licensed in China to test people for antibodies to the virus, to determine how many have been infected. Some may not have gotten sick. That test could also show whether people who did get sick are immune from reinfection.

Can face masks protect you?

28365365体育投注Health experts and mask makers say only a properly used reusable N95 respirator mask certified by an independent agency can guard against the virus. Paper or polyurethane foam masks don’t filter out smaller particles responsible for transmitting infectious agents. They might help prevent sick people from transmitting to others.

How Effective Are Masks?

The World Health Organization and other experts report that a mask's efficacy in social settings is inconclusive. But some health experts and mask makers say that properly used, the N95 respirator mask can guard against the new coronavirus.

Airborne

Large droplets

Surgical masks are highly effective against large airborne droplets.

39.9”

Approx. distance

large droplets can travel

Small droplets

These traditional masks are less effective with small droplets, as they can travel farther and in unpredictable paths affected by wind and other gusts. The droplets can be inhaled around the sides of the masks.

Touch

A coronavirus can also be transmitted by touching an object where airborne droplets have settled.

28365365体育投注The viruses can survive briefly on surfaces depending on conditions of humidity and temperature.

28365365体育投注Wearing a mask prevents direct contact with nose and mouth, and could protect a user who may have touched a contaminated area.

Masks

Frequently changing disposable masks, and washing your hands after, are important steps to avoid contamination from pathogens that cling to the outer surface.

N95 masks28365365体育投注 offer more protection. But they only work if they fit properly, and aren’t suitable for children or people with facial hair.

Surgical masks28365365体育投注 don’t offer full protection against airborne viruses. They don’t fully seal off the nose and mouth.

Airborne

Large droplets

28365365体育投注Surgical masks are highly effective against large airborne droplets.

39.9”

Approx. distance

large droplets can travel

Small droplets

These traditional masks are less effective with small droplets, as they can travel farther and in unpredictable paths affected by wind and other gusts. The droplets can be inhaled around the sides of the masks.

Touch

28365365体育投注 A coronavirus can also be transmitted by touching an object where airborne droplets have settled.

28365365体育投注The viruses can survive briefly on surfaces depending on conditions of humidity and temperature.

Wearing a mask prevents direct contact with nose and mouth, and could protect a user who may have touched a contaminated area.

Masks

Frequently changing disposable masks, and washing your hands after, are important steps to avoid contamination from pathogens that cling to the outer surface.

N95 masks offer more protection. But they only work if they fit properly, and aren’t suitable for children or people with facial hair.

Surgical masks28365365体育投注 don’t offer full protection against airborne viruses. They don’t fully seal off the nose and mouth.

Airborne

Large droplets

Surgical masks are highly effective against large airborne droplets.

39.9”

Approx. distance

28365365体育投注large droplets can travel

28365365体育投注Small droplets

28365365体育投注These traditional masks are less effective with small droplets, as they can travel farther and in unpredictable paths affected by wind and other gusts. The droplets can be inhaled around the sides of the masks.

Touch

28365365体育投注 A coronavirus can also be transmitted by touching an object where airborne droplets have settled.

The viruses can survive briefly on surfaces depending on conditions of humidity and temperature.

Wearing a mask prevents direct contact with nose and mouth, and could protect a user who may have touched a contaminated area.

Masks

Frequently changing disposable masks, and washing your hands after, are important steps to avoid contamination from pathogens that cling to the outer surface.

N95 masks offer more protection. But they only work if they fit properly, and aren’t suitable for children or people with facial hair.

Surgical masks don’t offer full protection against airborne viruses. They don’t fully seal off the nose and mouth.

Airborne

28365365体育投注Large droplets

Surgical masks are highly effective against large

airborne droplets.

39.9”

28365365体育投注Approx. distance

large droplets

can travel

Small droplets

These traditional masks are less effective with small droplets, as they can travel farther and in unpredictable paths affected by wind and other gusts. The droplets can be inhaled around the sides of the masks.

Touch

A coronavirus can also be transmitted by touching an object where airborne droplets have settled.

The viruses can survive briefly on surfaces depending on conditions of humidity and temperature.

28365365体育投注Wearing a mask prevents direct contact with nose and mouth, and could protect a user who may have touched a contaminated area.

Masks

Frequently changing disposable masks, and washing your hands after, are important steps to avoid contamination from pathogens that cling to the outer surface.

Surgical masks don’t offer full protection against airborne viruses. They don’t fully seal off the nose and mouth.

N95 masks offer more protection. But they only work if they fit properly, and aren’t suitable for children or people with facial hair.

Sources: BMC Infectious Diseases; The Journal of Hospital Infection

Research: Lindsay Huth and Taylor Umlauf Graphic: Alberto Cervantes/THE WALL STREET JOURNAL

What else can I do to protect myself?

The most important thing you can do is wash your hands frequently, for at least 20 seconds each time. Wash them regularly when you are at the office, when you come home, before you eat, and other times that you are touching surfaces. You can also use an alcohol-based hand sanitizer. Don’t touch your eyes, nose or mouth—viruses can enter your body that way. Wipe down objects and surfaces frequently with household cleaner, which will kill the virus. Maintain a distance from people who are sick.

Get a flu shot, if you didn’t get one already. Stock up on some supplies in case you have to stay home, infectious-disease experts say. To avoid cleaning out store shelves, just buy a few extras on your regular orders or trips to the store. Items to consider include shelf-stable foods like cans of beans, packages of rice and pasta, and beverages; pain relievers and other common medications; extra prescription medications; and hygiene and cleaning products.

A Public Health England sign warning passengers at London’s Heathrow Airport of the virus.

Photo: daniel leal-olivas/Agence France-Presse/Getty Images
Can you catch the virus from someone even before they have symptoms?

It is possible. But little is known so far. In Macau, a 15-year-old resident of Wuhan, the epicenter of the outbreak, tested positive for the coronavirus despite having no fever or cough, according to that special administrative region of China. Scientists reported in the Lancet medical journal that they identified the coronavirus in a 10-year-old boy who developed no symptoms, even though others in the child’s family fell ill. Chinese news outlets have reported a handful of other potential asymptomatic cases.

How the First Patients Fared

By Jan. 2, Researchers identifed 41 novel coronavirus patients who had been admitted to the hospital in Wuhan, China.

MOST COMMON EARLY SYMPTOMS

Fever

98%

Cough

76

28365365体育投注Aches, fatigue

44

28365365体育投注HOW THE DISEASE PROGRESSED

Avg. days since

onset of symptoms

7

8

9

10.5 days

Admitted

28365365体育投注to hospital

Acute

respiratory

distress

28365365体育投注No. of patients

41

21

11

16

Admitted

28365365体育投注to intensive

care unit

Shortness

of breath

OUTCOMES*

Out of 41 patients

2828365365体育投注 Discharged from hospital

7 Still hospitalized

6 Died

*As of Jan. 22, roughly 20 days after coronavirus diagnoses confimed Source: The Lancet

Can you get infected after you’ve already had the disease?

That isn’t yet known. Sometimes a person is immune to a disease after an infection, but not always. Blood tests that reveal how many antibodies people who have recovered have will shed some light on the prospects for immunity.

How worried should I be?

Most people who are infected might become only mildly ill, data suggest. But “mild” can be anything from a fever, cough and aches to pneumonia that doesn’t become too severe. So for most people it is probably not just a few sniffles. And mild or not, you’ll have to be isolated or quarantined.

28365365体育投注By not getting infected, you’ll also protect those around you, including older family members or anyone you know with heart disease or diabetes, conditions that increase risk of severe illness.

Of 44,672 cases in China, 81% had mild symptoms, 13.8% were severely ill, and 4.7% were critically ill, according to the Chinese CDC. All of those who died were in critical condition.

Public-health officials are trying to determine how many people have been infected, including those who didn’t get sick at all. They are concerned and want to contain the virus because its effects aren’t fully known. In addition, new viruses can mutate, possibly becoming more virulent as they work their way through a population.

Where did the new coronavirus come from?

28365365体育投注The new virus likely came originally from bats, scientists say. It isn’t known exactly where or how it jumped to humans, though. Viruses from bats often infect another mammal first and then mutate to become more transmissible to humans. One hypothesis is that the intermediary animal for this new virus may be a pangolin, a small mammal sold in wildlife markets, prized for its meat and scales covering its body.

SHARE YOUR THOUGHTS

Do you have questions about the risk of the new coronavirus from China? Join the conversation below.

Health officials believe the outbreak originated in a large animal and seafood market in Wuhan, China.

Of the first 41 cases, 27 had some exposure to that market, according to a report in the Lancet. But three of the first four people to become ill, on Dec. 1 and Dec. 10, said they had no contact with the market.

A study in the New England Journal of Medicine found that 55% of patients in Wuhan who became ill before Jan. 1 had a link to the market, compared with 8.6% of those who became ill after that point. Scientists say it will take some time to identify the exact source.

Is the virus mutating, particularly in a way that would make it more contagious?

28365365体育投注No. The virus has remained stable genetically thus far, according to the WHO and the U.S. CDC.

Related Video

As the coronavirus threatens to spread across the U.S., federal health authorities expand the criteria for whom should be tested and streamline test-kit approvals. Photo: Jeenah Moon/Bloomberg

Is it safe to travel internationally?

The U.S. State Department has warned Americans to avoid or reconsider travel to countries where there are outbreaks of Covid-19. They include China, South Korea and Italy. Travelers to Japan are urged to exercise caution. Those who are in countries where outbreaks are occurring should stay home as much as possible, limit contact with others and follow guidelines from the CDC to prevent infection, U.S. authorities say.

Is it safe to go on a cruise?

The U.S. State Department has urged Americans to reconsider cruises to or within Asia, given the risk of infection and of being subjected to a lengthy quarantine.

A health official watching travelers on a thermographic monitor at the Sultan Iskandar Muda International Airport in Indonesia.

Photo: Zikri Maulana/SOPA Images/Zuma Press
Are there drugs to treat coronaviruses?

There aren’t any drugs or vaccines approved specifically for the new virus. But several are in development or being studied. Two clinical trials in China and one in the U.S. are evaluating remdesivir, an antiviral drug from Inc.28365365体育投注 that was also tested for Ebola.

A hospital in Wuhan is conducting a clinical trial using a combination of two drugs for HIV that had been tested on MERS patients in Saudi Arabia. The therapy, sold under the brand name Kaletra in the U.S., is normally used to treat HIV patients and belongs to a class of drugs known as protease inhibitors, which block a key enzyme that helps viruses replicate. In addition, a few vaccine makers are developing products targeting the virus.

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