Updated: Your most urgent questions about the new coronavirus

In this fast-evolving epidemic, even experts find many answers are not yet available

The medical staff at a community health station fill out a form for a woman (watching in coat) suspected of having 2019-nCoV. The woman will later be sent on to a hospital in Wuhan, China.

Feature China/Barcroft Media/Getty Images

Scientists are racing to unravel the mysteries of a new coronavirus that recently emerged in China. The outbreak is now a global public health emergency, the World Health Organization said on January 30. As of February 13, the virus had infected at least 60,000 people globally. It had killed at least 1,370 (all but 3 deaths have been in mainland China).

The germ’s rapid spread has sparked global concern. It also is triggering many questions from researchers and the public alike. In this rapidly evolving epidemic, many unknowns remain.

Scientists call the new germ 2019 novel coronavirus, or 2019-nCoV. On February 11, they started calling the disease it triggers COVID-19. We will update these answers as more information becomes available.  

Do you have questions about the new coronavirus that you’d like answered? E-mail them to feedback@sciencenews.org.

What is 2019-nCoV?

Coronaviruses are one of a variety of viruses that typically cause colds. But three members of this viral family have caused more severe outbreaks that include pneumonia (a type of inflammatory lung disease) and risk of death. The first was severe acute respiratory syndrome, or SARS. Then came Middle East respiratory syndrome, or MERS. Now there is 2019-nCoV. This latest coronavirus first emerged in Wuhan, China.

When did the outbreak start?

Chinese officials notified the World Health Organization on December 31, 2019 of an unknown pneumonia-like disease. It had been seen in 44 patients. Initial reports tied this disease to a seafood market in Wuhan, a city in central China’s Hubei Province.

But the earliest cases may not be related to exposure at the market. That’s what a team of Chinese researchers reported January 24 in The Lancet. The earliest known patient — the so-called “index case” — got sick December 1. He had not been exposed to the market, according to the study.

So far, versions of the new virus isolated from patients in China and other countries are very quite similar. “This lack of diversity fits with an origin in the human population in mid-November,” says Trevor Bedford. He’s an evolutionary biologist at the Fred Hutchinson Cancer Research Center and the University of Washington. Both are in Seattle, Wash.

“The market was not the [source of the] index case. It was an amplifier,” said Anthony Fauci. He said, “People crowded in the market infected each other.” Fauci directs the National Institute of Allergy and Infectious Diseases in Bethesda, Md. He was speaking at a Biothreats meeting in Arlington, Va., that was sponsored by the American Society for Microbiology.

Where did the virus come from?

Coronaviruses originate in wild animals. Sometimes they leap to humans.

Bats often carry coronaviruses. However, in most cases they don’t pass these viruses directly to people. SARS probably first jumped from bats into raccoon dogs or palm civets. People got sick only after making contact with those other animals. All the pieces necessary to re-create SARS are still circulating among bats, although that virus has not been seen in people since 2004.

MERS went from bats to camels. Later, it leaped to people. A paper published January 22 in the Journal of Medical Virology suggests that the new coronavirus has components from bat coronaviruses, but that snakes may have passed the virus to people. Many virologists, however, are skeptical that snakes are behind the outbreak.

Current data suggest that the virus made the leap from animals to humans just once. Since then it likely has been moving between people. Based on how closely related the viruses are that have been isolated from patients, Bedford says, animals from the seafood market probably didn’t give people the virus multiple times (as researchers once thought). If the virus leaped from animals to people many times, the researchers would expect there to be more genetic changes among them. Bedford and colleagues updated their conclusions and supporting data January 29 at nextstrain.org.

Can it infect pets?

There are currently no reports of pets getting sick with COVID-19.  

Several types of coronaviruses can infect animals. In some cases it can make them ill. So the U.S. Centers for Disease Control and Prevention, or CDC, advises avoiding contact with pets and wearing a face mask if you are sick. In 2003, researchers reported in Nature that cats could be infected with the SARS virus. Those cats could then spread the virus to other cats in the same cage. But the cats didn’t show symptoms. Ferrets, too, could get and share the virus. One difference: The ferrets became sick.  

While the CDC recommends that people traveling to China avoid animals, the agency says there is no reason to believe that animals or pets in the United States can transmit the virus.

What are the symptoms of a 2019-nCoV infection?

People with COVID-19 may develop a fever, cough and difficulty breathing, according to the CDC. These symptoms are similar to SARS, researchers reported January 24 in The Lancet. Though many COVID-19 patients might experience mild symptoms, others can develop pneumonia.

Based on how MERS works, the CDC reports that symptoms of 2019-nCoV may appear from two to 14 days after exposure. On average, it may take someone five days to become visibly sick, researchers reported January 29 in the New England Journal of Medicine. That number, however, is based on only 10 patients. So it needs further study, the researchers wrote.

How do doctors test for 2019-nCoV?

WHO laboratory testing guidelines suggest doctors take multiple samples from people they suspect might have become infected. Those samples could come from nose and throat swabs, from blood and from sputum from the lower respiratory tract.

In the lab, researchers look for genetic signs of the virus. They do this using a method called reverse transcription polymerase chain reaction, or RT-PCR. If the virus is present, the technique produces copies of RNA — the virus’s genetic code. This RNA signature is unique to SARS-like coronaviruses. For positive tests, researchers do further genetic analyses to pin down whether the virus is actually 2019-nCoV.

The method relies on patients being so sick that they host high amounts of the virus — enough of it to detect. Not everyone who is infected will have a positive test. “It isn’t like it’s a horrible test,” Fauci said at a White House news conference on January 31. “But it is not a test that’s absolute.”

Doctors previously had to ship samples to the CDC. They usually received results in three to five days, says notes Alexander Greninger. He’s a clinical virologist at the University of Washington in Seattle. In an effort to spped up testing, the U.S. Food and Drug Administration on February 4 approved an emergency use authorization. It now allows more than 200 CDC-qualified labs around the United States to also run the diagnostic test.   

How infectious is the virus?

Researchers don’t yet know. But since 2019-nCoV has never infected humans before last year, people have not yet developed immunity to it. So it’s likely that everyone is vulnerable to becoming infected.

How infectious a virus can be is described by what’s known as R0, or R naught. It is how many people each sick person tends to spread the virus to when a disease-causing organism hits a population where no one is immune, explains Maimuna Majumder. She’s a computational epidemiologist, someone who uses math to help track and investigate the spread of disease. She works in Massachusetts at Boston Children’s Hospital and Harvard Medical School.

Almost no virus spreads as far as its possible limits, Majumder says. “In general,” she says, “we don’t see transmission rates as high as the reproduction number would suggest.” For instance, people might wash their hands a lot. Or they might stay home to avoid getting sick. People who are sick may isolate themselves. All of these things could mean that a virus can’t reach its full potential for spread.

SARS has an R0 of 2.0 to 4.0. That means that each infected person had the potential to pass it on to two to four others. Generally, viruses with reproduction numbers greater than 1.0 may keep spreading if nothing is done to stop them. Outbreaks of viruses with an R0 that falls at or below 1.0 can eventually die out.

Several research groups have been working to pin down an R0 estimate for the new virus-based on outbreak information available to them and by harnessing different methods. Those other methods include computer models that simulate outbreaks or that make assumptions about a population’s susceptibility to the virus, potential exposure and infection rates. Others have used an approach that pulls data from current cases and allows the researchers to describe what is happening in real-time.

Current estimates vary, and some have already been revised. Majumder and her Harvard colleague Kenneth Mandl estimate the R0 for 2019-nCoV falls between 2.0 and 3.1. Meanwhile, Jonathan Read of Lancaster University in England and colleagues reported a R0 value on January 28 of 3.11 (with a range from 2.39 to 4.13) on medRxiv.org. But Christian Althaus and Julien Riou, both of the University of Bern in Switzerland, posted data to an online database and bioRxiv.org on January 24 that supports their calculation that the R0 is about 2.2 (with a range between 1.4 and 3.8).

Clearly, R0 is a tricky number to pin down, at least in an infection’s early days. It also can change as control measures are put in place. This suggests that as more cases emerge, these estimates will likely continue to shift. But currently the R0 appears to be similar to that for SARS.

How long does it stay on surfaces?

Researchers aren’t sure, but not very long. Or that’s what they expect, based on what they know about other coronaviruses. These viruses typically survive on a surface for only a few hours, notes Nancy Messonnier. She directs the CDC’s National Center for Immunization and Respiratory Disease in Atlanta, Ga. She spoke in a news conference on January 27.

While it’s still unclear how the new virus spreads, coronaviruses are thought to spread mainly by respiratory droplets. These are spewed as patients cough, for instance. There is no evidence suggesting 2019-nCoV can be transmitted from things such as imported goods, according to the CDC.

How does it spread?

The new virus is spreading from person to person in China and in several other countries. They include the United States. Like SARS and MERS, it probably spreads in much the same way as other respiratory diseases, the CDC says. Respiratory droplets from an infected person’s cough or sneeze can carry virus to someone new. Still, the exact mechanism of spread is unknown.

Some coronaviruses can cause the common cold. Severe coronaviruses infect deeper parts of the respiratory tract than cold viruses do. So infected people are not usually contagious until they start to show symptoms, says Stanley Perlman. He’s a virologist at the University of Iowa in Iowa City.

In previous outbreaks, “if somebody was going to get infected from [an] infected person, the virus had to get up into the upper airway so it could spread,” Perlman says. It wouldn’t spread until someone was sick enough to start coughing.

Unlike SARS and MERS, however, there have been some reports of people without symptoms spreading 2019-nCoV. That’s what Chinese officials first reported on January 26. On January 30, a report in the New England Journal of Medicine identified additional workers in Germany who had become infected by a visiting colleague from China who showed no symptoms. (That woman later told German officials she felt tired and achy, Science magazine reported on February 3.) One of her German colleagues then spread the virus to two other coworkers before that man became ill. He also showed high levels of the coronavirus in his nose and in his phlegm even after his mild symptoms had ended.

Because people might be infected and not show obvious symptoms, doctors should isolate patients and trace their contacts as soon as possible, researchers reported January 24 in The Lancet.

People with no symptoms can spread viruses such as those that cause influenza or measle. But this trait would be new for the types of coronaviruses that cause epidemics, Perlman says.

And this could make outbreaks of this virus hard to control. For instance, with no signs that people are sick, airport screenings would be less useful. The good news: Symptom-free people have never been the major driver of epidemics, said Fauci at a news conference on January 28.

How far has 2019-nCoV spread?

So far, it’s not clear how many people the virus has sickened. Epidemiologists — researchers who work as disease detectives — are attempting to come up with a good estimate.

Through the mid-February, most of the thousands of people with confirmed diagnoses of the new virus have been in China. But several other countries — 27 as of February 11 — also reported isolated cases. Many of these patients had just returned from a trip to China.

But those numbers are likely way low, researchers say. Symptoms don’t appear right away. That means many infected people may show no or mild symptoms,

Joseph T. Wu is an epidemiologist and biostatistician at the University of Hong Kong. He was part of a team that issued a report January 31 in the Lancet. It estimated that in the city of Wuhan alone, 75,815 people may have been infected as of January 25. Especially worrisome: The number of cases there appeared to be doubling, on average, every 6.4 days.

Wu’s group calculated that by late January, Wuhan had already exported 461 cases to Chongqing, 113 to Beijing, 98 to Shanghai and 111 to Guangzhou. Those cities now may become hubs for further spread.

Wu’s group also forecasted the epidemic’s future spread. If the virus continues spreading at the current rate, the epidemic could peak in Wuhan in April. It could peak in other Chinese cities a week or two later. Reducing transmission rates by one-fourth would slow the epidemic’s growth and delay when the outbreak peaked by about a month. It also might cut the total number of cases in half, the researchers estimated. To come up with these numbers, Wu’s team used exported case counts and data on people traveling in and out of China.

A few countries outside China are now reporting human-to-human transmission, including VietnamGermany and the United States (see below, What is the situation in the United States?).

What are the best containment methods?

It’s unclear. Health officials and governments have attempted to try to limit the spread of the new virus. In some areas outside of China, they shut down entire cities and put a mandatory quarantine in place for travelers coming from China. Experts remain skeptical, however, that such measures will help much.

Quarantines, especially at large scales, are largely ineffective and often have an effect opposite to what officials want, experts say.   

Allison McGeer is an infectious disease expert at Mount Sinai Hospital in Toronto, Canada. She contracted SARS in 2003 while taking care of patients. So she appreciates the risks posed by such potentially deadly coronaviruses. “This is an unprecedented situation,” she says. “Nobody knows what the right thing to do is.”

Quarantine and isolation were effective strategies to end the 2003 SARS outbreak. Still, experts don’t know whether similar methods will help control the new virus. Some quarantine efforts for the new outbreak have had favorable outcomes. Others have not.

After reports that some people without symptoms have spread the virus and with the growing number of cases in China, U.S. officials quarantined a group of 195 U.S. citizens. All had been evacuated from Wuhan, the CDC announced on January 31. The evacuees were held at March Air Reserve Base in Ontario, Calif. They had arrived on January 29. Their legally mandated two-week quarantine ended February 11. During that time, none tested positive for the new virus.

In another well-publicized case, passengers on a cruise ship were quarantined there, off the coast of Japan. This seems to have put certain people on board at higher risk of infection. In an environment like a cruise ship, it is hard to control the virus’s spread among passengers and among staff.

Eric Cioe-Pena directs global health at Northwell Health in New Hyde Park, N.Y. On February 12, he spoke with ABC NEWS. “The issue with quarantine remains the lack of ability in a closed environment like this to maintain infection prevention measures on a ship,” he said. “We are seeing numbers increase dramatically.” He said that likely points to ongoing spread of the virus on such ships. “That’s concerning,” he added, “as it’s creating a second epicenter of the infection in a Japanese port.”

Nearly 3,700 people were on board that quarantined cruise ship. At least 175 people had the virus, including 10 crew, Japan’s health ministry reported. The 14-day quarantine for these people was due to end on February 19. However, health officials said passengers and crew in close contact with newly diagnosed cases on the ship may have to stay longer. That was according to an NPR report on February 10. Another cruise ship was searching for a place to dock. But by February 12 it had been denied entry at multiple ports. This happened even though it did not have any sick people on board.

Some experts say keeping sick passengers and crew on boats is not necessary. “Let the passengers off and then quarantine them,” said Amesh Adalja on February 7. He works at the Johns Hopkins Center for Health Security in Baltimore, Md. There, he is a specialist in infectious diseases. He spoke to the news division of the Center for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis. At that time, he argued, quarantining a whole cruise ship is “an overreaction and it increases public fear to watch news reports of these ships.”

How deadly is the disease?

The coronaviruses that cause colds usually bring fairly mild symptoms. They tend to just affect the upper airways (sinuses and throat). But the new virus is more like SARS and MERS. It penetrates much deeper into the respiratory tract. 2019-nCoV is “a disease that causes more lung disease than sniffles,” says NIAID’s Fauci. It’s damage to the lungs that can make these viruses deadly.

An analysis of 99 hospitalized patients, including the first cases from Wuhan, shows that 17 developed what is known as acute respiratory distress syndrome. It’s a condition that affects the lungs and can limit the blood from getting enough oxygen. Eleven of these patients would go on to die from multiple organ failure. A team of 14 researchers in Wuhan and Shanghai, China, described the cases online January 29 in The Lancet.

The 2003 SARS outbreak killed nearly one in every 10 of the 8,000 people it sickened. MERS, a disease that still circulates in the Middle East, is more deadly. It kills about three in every 10 infected people. Right now, 2019-nCoV seems less virulent. Its death rate appears to be about two in every 100 infected people. That’s what the World Health Organization reported on January 23. But that number is may well change as more cases are diagnosed, Fauci notes.

“Almost certainly,” Fauci said at the Biothreats meeting, some people may be infected with the virus but won’t show symptoms. For now, he notes, “We don’t know at what level yet.” Right now, the outlook seems grim because health officials only know about people who are sick enough to come to the hospital. Some of those people die. Often those people who die had weak immune systems that couldn’t fight the virus. Or they might have had other diseases or conditions that make them more vulnerable.

More widespread screening may show exactly how many people get the virus but have mild or no symptoms. That will help researchers calculate how deadly the virus actually is.

Who is most likely to develop severe disease?

Researchers have made a study of detailed data from about 17,000 COVID-19 cases. Of these, 82 in every 100 showed only mild symptoms. That’s what WHO reported in a February 7 news conference. Another 15 in every 100 cases have been severe. Three more in every 100 become critically ill — and 2 in every 100 have died, officials note.

Most of the people with severe illness are older or were already sick with something else, according to the WHO. Overall, cases in children have been rare, researchers reported February 5 in JAMA.

What is the situation in the United States?

As of February 4, health officials had confirmed the coronavirus in 11 people. These included two infected by someone else in the United States.

Twenty U.S. airports began actively screening travelers from China for symptoms in late January. Because of the relatively rapid release of information from China, countries like the United States have had time to put strong screening procedures in place. This may have helped them keep the virus from spreading more, says Allison McGeer. She’s an infectious disease expert at Mount Sinai Hospital in Toronto, Canada. And as someone who contracted SARS in 2003 while taking care of patients, she knows personally the dangerous side of coronaviruses.

On January 31, the CDC announced that with the growing number of cases in China, U.S. officials had quarantined a group of 195 U.S. citizens. These people had been evacuated from Wuhan. The evacuees had landed at an Air Reserve Base in Ontario, Calif., two days earlier. They would stay for at least two weeks as their health was checked. The goal, explained CDC’s Messonnier, was “to prevent, as much as possible, community spread with this novel virus in the United States.”

What are the best ways to protect yourself?

There is no drug or vaccine to treat or prevent 2019-nCoV. But there are things people can do to limit the chance they will become infected. And they aren’t much different from what you’d do to keep from picking up colds or the flu, the CDC says. Wash your hands with soap and water for at least 20 seconds. (For perspective, that’s a little longer than it takes someone to sing the Happy Birthday song at a somewhat slow pace.) Other tips include covering your mouth when you cough or sneeze (or coughing or sneezing onto the floor if no handkerchief or tissue is available). Finally, don’t touch your eyes, nose or mouth. Who knows what viruses might have been on surfaces (such as stair railings or door handles) that you touched.

A couple years ago, Science News for Students staff writer Bethany Brookshire did a DIY Science experiment to test how far sneezed-out germs might go. Her data showed that germ-studded snot droplets might land 250 to 400 centimeters (8.2 to 13.1 feet) away from a sneezer. In her report, she also cited a 2016 study. It found that large snot droplets could travel 2 meters and less-viscous thin snot droplets could fly up to 8 meters (more than 26 feet). Stand clear!

To test how far sneezed-out germs might travel, Science News for Science staff scientist Bethany Brookshire put together an experiment. Here she explains how she conducted this snot science.

CREDIT: SSP/EXPLAINR

What about masks? It makes sense that they should help limit the spread of coughed or sneezed-out viruses. Certainly, McGeer says, “If you’re infected and you wear a mask, you’ll shed less virus into the air around you.” That puts less out there for others to encounter. But it’s not clear how much they’ll help healthy people, she says. Few of them seal around the nose and mouth. So that leaves plenty of room for airborne germs to be inhaled.

Tina Hesman Saey, Jonathan Lambert, Aimee Cummingham and Erin Garcia de Jesus contributed to reporting of this story.

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