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n outbreak of viral pneumonia that began in the central Chinese city of Wuhan at the end of 2019 has sickened more than 200,000 people and led to more than 8,000 deaths worldwide, as of March 18. (See the latest figures here.)

Scientists have made rapid progress in understanding the culprit, a new virus in the coronavirus family, which has been named severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2. The pneumonia-like disease it causes is called COVID-19.

As the virus has spread, however, misinformation has, too. We’ve written about many bogus claims about the new coronavirus spread through social media, as well as false and misleading claims made by politicians. See our Coronavirus Coverage page for a guide to our articles.  

Here, we answer some key questions about what is known so far about the outbreak and the virus.
When did the outbreak begin, and what is the cause?
Scientists are still working to determine when the virus first emerged in people, but the earliest known instances of the disease occurred in early December in Wuhan, a city of 11 million in central China. 

After a string of mysterious pneumonia cases, many of them linked to a seafood market selling wild game and live animals, officials reported the outbreak to the World Health Organization on Dec. 31.

By Jan. 7, Chinese authorities had isolated a virus, later named SARS-CoV-2, as the cause of the disease, and shared the genome a few days later. This allowed other countries to test for the virus, and for scientists to begin devising treatments and investigating how the outbreak began.

Coronaviruses are a diverse family of large RNA viruses that have characteristic spikes on their surface, making them look like they have a halo, or corona, when viewed under a microscope.

Most coronaviruses that infect humans are relatively benign and cause mild respiratory diseases such as the common cold, said Susan Weiss, a coronavirus researcher at the University of Pennsylvania, in a phone interview. 

But in recent years, new coronaviruses have cropped up that are far more dangerous to humans, including the severe acute respiratory syndrome, or SARS, virus, which led to a global outbreak in 2003, and the Middle East Respiratory Syndrome, or MERS, virus, which was identified in 2012.

According to the WHO, SARS ultimately infected more than 8,000 people, killing 774. Since 2012, there have been nearly 2,500 MERS cases and 858 deaths.

The new virus is fairly similar to the SARS virus — and is in the same betacoronavirus subgroup as both the SARS and MERS viruses — but is considered a new pathogen.

What are the symptoms, and how severe is the disease?
The virus causes a pneumonia-like respiratory illness that varies in severity, but can be deadly. Symptoms include fever, cough and shortness of breath. 

A report in the Lancet that analyzed the first 41 people admitted to the hospital for COVID-19 infection suggests that clinically, the illness is similar to SARS, although fewer patients appear to have diarrhea or upper respiratory symptoms, such as sneezing, a runny nose and sore throat. 

Some people also report fatigue, and in some cases people have been found to be infected, but clear of any symptoms. 

Many of the symptoms are common to other respiratory diseases. Lab tests based on the virus’ genetic sequence can confirm infection.

It’s not yet known how frequently people die from COVID-19. The reported fatality rates have fluctuated as the disease has spread, hovering around 2-3% in late January, and around 4% as of March 18. For comparison, SARS killed around 10% of infected people, if not more, while seasonal influenza typically kills 0.1% or less, David Fisman, an epidemiologist at the University of Toronto, said in an email.

But these estimates, which are simple calculations of the number of deaths relative to the number of known cases, may not accurately reflect how dangerous the virus is, since the disease course is still underway for many patients, Fisman said. It’s also likely that far more people have been infected, but have not gone to hospitals or had their illnesses confirmed. For example, if two-thirds of cases are unreported, he said, the case fatality rate may be significantly lower. (For more on the fatality rate, see our March 5 story “Trump and the Coronavirus Death Rate.”)

According to a February study by the Chinese Center for Disease Control and Prevention, 14% of cases in mainland China were severe and 5% were critical.

Reports indicate that while healthy people can fall seriously ill and die, deaths are primarily in older folks and those with preexisting conditions such as diabetes, cardiovascular disease, chronic respiratory conditions and hypertension.

The Chinese CDC study, for instance, found a mortality rate of 14.8% in patients 80 and older and 8% for those 70 to 79, while the overall fatality rate then was 2.3% for cases in mainland China.

Similar statistics from Italy bear out this trend. As of March 15, no one in the country below the age of 30 had died from COVID-19, but a fifth or more of those above age 80 with the disease had. In Italy, about 25% of cases have been severe.

How is the virus transmitted, and how contagious is it?
The Centers for Disease Control and Prevention says the new coronavirus is transmitted from person to person in close contact, within about 6 feet of one another.

Scientists suspect the transmission is similar to how influenza is spread, with the virus travelling through respiratory droplets when infected people cough or sneeze. This is how scientists believe past coronaviruses such as SARS and MERS have spread.

The incubation period, or how long before someone who is infected shows symptoms, is estimated to be around 4 days, but may range from 2 to 14 days, according to the CDC. There is some evidence that asymptomatic people can transmit the virus to others. A March 16 Science study that modeled how the outbreak unfolded in China also found that people who have few or no symptoms may be responsible for the bulk of the disease spread. The CDC, however, says that people are “thought to be most contagious when they are most symptomatic” and that asymptomatic people are “not thought to be the main way the virus spreads.”

It also could be possible to contract the disease by touching a contaminated surface and then touching your mouth, nose or even eyes. A study released in mid-March by scientists with the National Institutes of Health, CDC, UCLA and Princeton found the virus could be detected for up to 24 hours on cardboard and much longer on hard surfaces including plastic and stainless steel — for up to two to three days.

At a March 18 press conference, coronavirus task force coordinator Dr. Deborah Birx said that “we’re still working out how much is it by human-human transmission and how much is it by surface,” adding that the fundamental guidelines are to avoid exposure to “excess number of persons who could be asymptomatic and infected … and don’t expose yourself to surfaces that could have had the virus on it.”

It’s also unclear exactly how infectious the new virus is. Several groups of scientists have attempted to estimate SARS-CoV-2’s basic reproduction number, or R0, which is the average number of other people one person infects, assuming everyone in the population is susceptible.

Using a variety of methods, multiple teams have arrived at figures that generally range from 1.5 to 4, which suggest the transmissibility is roughly in line with that of SARS, but below that of the measles virus, which has an R0 of around 12 to 18, and is one of the most infectious viruses in the world.

“Despite the diversity of approaches taken there’s remarkable consistency in estimates from highly competent investigators, which seem to fall between 2 and 3,” said Fisman.

An early estimate from the WHO, for example, suggested that every infected person would spread the virus to 1.4 to 2.5 people, on average, while a team at Imperial College London pegged the R0 at 2.6. A group at the University of Bern in Switzerland calculated an R0 of 1.4 to 3.8, and Harvard researchers Maia Majumder and Kenneth Mandl estimated a figure between 2 and 3.1.

While the figures provide some clue as to how contagious the virus is, it’s important to recognize that these values don’t necessarily say anything about how widespread the outbreak will be. 

As Majumder pointed out on Twitter, the R0 reflects potential transmission, not actual transmission — and that even though seasonal flu has a relatively low R0 of about 1.3, it causes millions of cases per year, whereas SARS had an R0 between 2 and 5, and led to fewer than 10,000 cases.

“Planning, preparedness, and infection control can effectively bring an outbreak of a novel, moderate-R_0 disease to a close even in the absence of vaccines,” Majumder said in a tweet. “Because of this, estimates of R_0 for #nCoV2019 should be viewed as a call to action instead of a reason to panic.”

How can people protect themselves from contracting or spreading the virus?
The CDC advises people to wash their hands frequently, with soap and water for a minimum of 20 seconds, avoid touching their faces with unwashed hands, avoid close contact with sick individuals, and avoid social interactions generally to prevent community spread.

The CDC website provides advice on what to do if you’re sick and other resources.
This text is objective. The text features facts and statistics from reputable sources, and the tone of the text is unemotional, strictly conveying information. It appears there is no bias from the author in presenting the facts. Additionally, the use of direct quotes suggests research has been done on the topic.