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.
What is a coronavirus?
This virus belongs to a family of viruses 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.
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. Other reported symptoms include fatigue, sore throat, headache, and nausea, with vomiting and diarrhea. Some people 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.
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.
The mortality rate has differed by region, according to a report by an international mission of experts led by the World Health Organization to China. The mortality rate was 5.8% in the first several weeks in Wuhan, China, where the epidemic originated. But in other, less hard-hit areas of China, which had more time to prepare to care for patients, it was 0.7%. The rate in China has come down over time, the report said.
The overall mortality rate may be less than 1%, U.S. health officials suggested recently in the New England Journal of Medicine, if the number of asymptomatic or mildly ill cases is several times greater than that of reported cases.
That is still deadlier than seasonal flu, which has a mortality rate of about 0.1%.
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. Covid-19 is far less deadly than MERS or Ebola.
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?
Adults of all ages have been infected, but the risk of severe disease and death is highest for older people and those with other health conditions such as heart disease, chronic lung disease, cancer and 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. Of the children who were infected in China, only a small proportion were severely ill, according to the WHO.
How at risk is someone in the U.S.?
The current risk to the U.S. public is low, the U.S. Centers for Disease Control and Prevention says. The virus isn’t believed to be spreading widely. But there have been localized outbreaks, such as in the Seattle area and the number of nontravel-related cases is growing.
The CDC says it expects the virus to spread more widely in the country. Federal and local health officials are preparing for that likelihood and urging the public to prepare to take precautions and for possible business and school closures. Some schools have been closed and events canceled proactively.
How is the virus spread among humans?
It transmits through “respiratory droplets” when an infected person speaks, coughs or sneezes, according to the WHO. 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 like a desk, counter, or doorknob, where they can survive for a period. A person can become infected by touching a contaminated surface, then touching their mouth, nose or eyes.
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. The WHO has said it doesn’t believe so-called fecal-oral transmission to be a driver of transmission of Covid-19.
How long can the virus survive on surfaces?
It is not clear, the WHO says. A recent review of 22 studies found that coronaviruses can last on surfaces such as metal, glass or plastic from two hours up to nine days. Some of the viruses survived shorter periods in warmer temperatures of 30 degrees Celsius or more, according to the review. Wipe down countertops, doorknobs and other commonly touched surfaces frequently. Regular household disinfectant wipes and cleaners kill these viruses.
How easily does the virus spread?
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.
Public-health experts caution that these estimates are preliminary, change over time and can be lowered by measures to prevent the virus from spreading.
Experts are debating how easily the virus is transmitted. The WHO-led mission of experts who visited China reported that clusters of transmission occurred largely in families, suggesting close contact. Other outbreaks suggest more widespread patterns.
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 new coronavirus or another infection. Right now in the U.S. a test is hard to get. 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 may have the disease. Hundreds of thousands of people have been tested in China and South Korea. In the U.S., testing was limited by a snafu and narrow testing criteria. Now, more tests are being distributed and the CDC says doctors may decide whether a patient should be tested.
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?
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.
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.
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.
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.
Can you catch the virus from someone even before they have symptoms?
It is possible. But little is known. The proportion of asymptomatic cases appears to be rare, and not a major factor in transmission of Covid-19, according to the WHO report from the mission to China. Most asymptomatic cases that have been reported went on to develop symptoms, the report said.
Still, cases have been documented. In Macau, a 15-year-old 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.
Can you get infected after you have 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.
By not getting infected, you would 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.
What if I have to self-isolate?
If you are told to self-isolate, you will need to stay at home and avoid contact with others for 14 days. Try not to stay in the same room with others at the same time, the U.K’s National Health Service recommends. Stay in a well-ventilated room with a window that can be opened. Don’t share towels, utensils or dishes with others, and wash them thoroughly after use. Clean bathrooms and surfaces regularly. Wash your hands before and after contact with pets.
Don’t go out to public places; ask family members or friends to get groceries, medicines and other supplies for you. Ask delivery people to leave items outside.
Where did the new coronavirus come from?
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.
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?
No. The virus has remained stable genetically thus far, according to the WHO and the U.S. CDC.
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.
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 Gilead Sciences Inc. 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.
Could imported goods carry the virus?
That is unlikely, the CDC says. Coronaviruses generally don’t survive that long on inanimate surfaces, according to the agency.