Editor’s note, April 2: There have been significant developments in the coronavirus pandemic since this story was last updated. Here is our latest information on the big questions about the coronavirus, as of this writing. For our most up-to-date coverage, visit our coronavirus hub.

The coronavirus outbreak, which began in China, keeps evolving at a dizzying speed. With the global case toll rising steeply, face masks flying off store shelves, borders around the world closing, and meetings, cruise itineraries, and the global economy upended by the virus, it’s no wonder questions and fears are swirling about Covid-19, as the disease is known.

On March 11, the WHO declared the outbreak a pandemic, a new disease that has spread around the world. Many countries have seen reported cases of the virus rise within their borders — and that includes the US.

“We will see more cases, and things will get worse,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told members of the House Oversight Committee on March 11. “How much worse … will depend on our ability to do two things: to contain the influx in people who are infected coming from the outside and the ability to contain and mitigate within our own country.”

Spread of the virus and the slow rollout of testing mean reported case numbers are changing quickly. Meanwhile, outbreaks have been surging in South Korea, Italy, and Iran. With the new virus continuing its tour around the world, here are answers to your most burning questions.

1) What is this new coronavirus, and where did it come from?

Coronaviruses are a large family of viruses that typically attack the respiratory system. The name comes from the Latin word corona, for crown, and the ancient Greek korōnè, meaning garland or wreath, because of the spiky fringe encircling these viruses. Most coronaviruses infect animals, such as bats, cats, and birds. Only seven, including Covid-19, SARS, and MERS, are known to infect humans.

SARS is thought to have evolved from infecting bats to civet cats to humans in China; MERS evolved from bats to camels to humans in the Middle East. No one knows precisely where Covid-19 came from, though a leading hypothesis is that bats were once again the original source: They spread the virus to another animal species, possibly a pangolin, where it jumped to humans.

2) What are the symptoms and death rate?

Two of the seven coronaviruses that infect humans, SARS and MERS, can cause severe pneumonia and even death in 10 and more than 30 percent of cases, respectively. But others lead to milder symptoms, like a common cold. The most common symptoms of Covid-19 are fever and dry cough.

No one knows the precise incubation period for the virus, but symptoms can show up anywhere from one day to two weeks after exposure, according to a WHO report on China’s response.

At the moment, we know Covid-19 can cause pneumonia and that it too can kill — but while it seems to be less deadly than SARS and MERS, it’s not yet clear by precisely how much.

Some of the best evidence on the question comes from a February 16 China Center for Disease Control report looking at the outcomes of the first 72,314 patients with confirmed or suspected Covid-19 in mainland China. It’s the largest such analysis to date, and it found an overall case fatality rate of 2.3 percent — lower than both SARS and MERS. (The case fatality rate, or CFR, is the proportion of deaths a disease causes within a group of people who have the disease.)

The researchers also discovered a huge variation in the case fatality rate by age group. In short, the virus appears to be deadlier in people with each passing decade. You can see the trend in this graph:

Overall, the researchers characterized 81 percent of the cases as mild and 19 percent as severe or critical.

One major caveat, though: This data comes from mainland China. And the case fatality rate has been different outside of China.

At the same time, there’s also evidence of asymptomatic cases. And it’s possible that as we discover more of these cases, Covid-19 will look less deadly. That’s because infectious diseases typically look more severe when they’re first discovered since the people showing up in hospitals tend to be the sickest. Disease modelers who account for this under-counting of cases currently estimate an overall case fatality rate of just over 1 percent.

As for symptoms: Fever, dry cough, and fatigue are more common, while thick mucus from coughs, shortness of breath, sore throat, and headache are less common, according to China’s data.

But the picture might change as data on symptoms emerge from other countries. For example, a yet-to-be published German paper looked at some of the country’s earliest confirmed Covid-19 patients. Researchers found symptoms in this small sample often resembled a cold. So only two of the nine patients had a fever, and seven had a cough, but just as common were symptoms like stuffy nose, runny nose, and sneezing.

3) What should I do if I think I have Covid-19?

If you’re in a high-risk group — over the age of 60 with an underlying health condition — seek medical treatment immediately, and let your hospital or health care provider know you suspect Covid-19 before showing up.

Otherwise, stay at home and call a health professional, Vox’s Umair Irfan explained: “They will work with your local health department and figure out whether you need to get tested or get treatment. Doctors and health officials advise not to go to the emergency room if your symptoms do not appear to be life-threatening.” There’s a good chance you’ll recover with nothing more than rest and fluids. But you will need to self-isolate while sick to avoid spreading the disease to others, including any people in your home. Here’s how to do it.

The CDC recommends several measures to help prevent the spread of Covid-19: Wash your hands often for at least 20 seconds.

Cover your cough or sneeze with a tissue, then throw it in the trash.

Clean and disinfect frequently touched objects.

Stay home as much as possible, and do not go out if you are sick.

Wear at least a cloth mask in certain public settings.

Contact a health worker if you have symptoms. Guidance may change. Stay informed, and stay safe, with Vox’s coronavirus coverage hub.

And if you are healthy, here are some ways you can help vulnerable people in your community.

4) How do coronaviruses spread?

We don’t yet know exactly how SARS-CoV-2 — the virus that causes the Covid-19 disease — spreads, but we do have a lot of data on how MERS, SARS, and other respiratory viruses move from person to person. And that’s mainly through exposure to droplets from coughing or sneezing.

So when an infected person coughs or sneezes, they let out a spray, and if these droplets reach the nose, eyes, or mouth of another person, they can pass on the virus, said Jennifer Nuzzo, an infectious disease expert and senior scholar at the Johns Hopkins Center for Health Security. In rarer cases, a person might catch a respiratory disease indirectly, “via touching droplets on surfaces — and then touching mucosal membranes” in the mouth, eyes, and nose, she added.

There’s also emerging evidence showing that SARS-CoV-2 may spread through poop — known as the “fecal-oral” route of disease transmission. Researchers are on the lookout for potential airborne transmission, too, and there’s a lot of speculation about whether inanimate objects — like door handles — can pass on the virus.

In the case of airborne transmission, a person would get infected by directly inhaling droplets suspended in the air from an infected individual. With “fomites” — objects that can transmit infections — droplets from an infected person would end up on surfaces another person touches. “So far, there is no conclusive evidence of that,” wrote Megan Murray, a Harvard Infectious Disease specialist, in a coronavirus explainer, “although that is challenging to prove one way or the other.”

What we do know: More and more research is piling up to suggest people who have only mild symptoms, or no symptoms at all, can test positive for Covid-19 disease. The virus also appears to be present in the body at very high levels early on in an illness, when people are still going to work or traveling.

“We still don’t know to what extent people without symptoms can infect,” Nuzzo cautioned. And Isaac Bogoch, a professor at the University of Toronto told Vox, “even if there have been cases of asymptomatic transmission of this infection, those will be typically rare cases, and with just about every other respiratory tract infection known to humankind, those are not the people who are driving an epidemic.”

Even so, if this virus can spread from people with no or mild symptoms, it might help explain why it’s so contagious. Researchers currently believe one person with Covid-19 generally infects two to more than three others, which would make the new coronavirus more transmissible than seasonal flu, SARS, and MERS. That’s why social distancing measures are so important.

5) What should I do to protect myself? Buy a face mask?

In the US, just about every health expert Vox has spoken to has said there’s little evidence to support the use of face masks for preventing disease in the general population.

Masks are only useful if you have a respiratory infection already and want to minimize the risk of spread to others, or if you’re caring for someone who is sick or working in a hospital in direct contact with people who have respiratory illnesses. (Plus, there are reports of runs on masks and other supplies that health workers need to stay safe. If they can’t get them and start walking off the job, we’re all in trouble.)

Related How soap absolutely annihilates the coronavirus

That’s why the CDC advises against the use of masks for regular Americans. The best thing you can do to prevent all sorts of illnesses, CDC’s Nancy Messonnier said, is “wash your hands, cover your cough, take care of yourself, and keep alert to the information that we’re providing.”

Individuals at a higher risk of developing severe disease — the elderly, people with underlying health conditions — should take additional precautions: avoiding crowds and contact with people who are sick, and stocking up on medicines and groceries, Messonnier said.

6) Is this a deadly pandemic?

The WHO has officially declared the outbreak a pandemic, with the disease in more than 100 countries and major epidemics in several regions of the world.

That means containing the virus — fully halting its spread — is no longer the goal but rather mitigation of fast spread and harm reduction.

Keep in mind, the p-word doesn’t say anything about the severity of Covid-19. A disease can spread widely and become a pandemic without being particularly severe. And no one knows yet what the ultimate effects of this pandemic will look like — mostly because we don’t yet know precisely how lethal the disease is.

There was a time when it seemed possible that China might contain the virus and the outbreaks outside of China would fizzle out, spelling the end of this public health emergency.

But there are now so many around the world, and the very real possibility that the virus is circulating, undetected, in even more countries — especially those with weak health systems — that containment appears out of reach.

This means we’re likely to see more sickness and death in many countries as cases grow from one-off travelers or small clusters to full-blown outbreaks.

In this scenario, the NIH’s Fauci said, “you don’t try to control [the virus] because it’s already everywhere.”

Health officials are now in the mitigation phase of the response strategy. This involves a focus on social distancing to slow the speed of the outbreak and avoid overwhelming health systems. It also involves ramping up public health communications to inform the public about the disease, testing of potential cases to find sick people and their contacts, and capacity in hospitals.

So hospitals need to be ready with Covid-19 protocols so the disease doesn’t spread from them, and health care workers need to be protected with access to protective equipment such as face masks so they can keep doing their jobs. Countries also need plans in place for maintaining supply chains and carrying on with travel and trade.

The slow rollout of testing in the US, in particular, has made slowing the spread of the virus more difficult.

An investigation led by the Atlantic and independent researchers found that a little more than 7,000 people in the US had been tested as of March 11 — putting the US far behind other developed countries. (The Covid Tracking Project team is now gathering test counts daily.)

Slowing epidemics is critical in preventing more deaths, as it reduces stress on hospitals and health centers, which can only treat a certain number of patients at a time. That’s why “flattening the curve” of the pandemic through social distancing measures is so important.

As Eliza Barclay and Dylan Scott wrote for Vox: “A disastrous inundation of hospitals can likely be averted with protective measures we’re now seeing more of — closing schools, canceling mass gatherings, working from home, self-quarantine, self-isolation, avoiding crowds — to keep the virus from spreading fast.”

In the best-case scenario, which has become less likely, this outbreak might look more like H1N1 swine flu. When H1N1 was first recognized in 2009 and spread around the world, there were major concerns about its lethality. US schools closed, people from North America were quarantined when they arrived in other countries, flights were canceled. Not only did those measures fail to contain the virus, Nuzzo said, but it also turned out H1N1 wasn’t all that deadly.

“Now we’re still living with that virus — it’s one that circulates with every flu season,” Nuzzo explained.

7) Are there any places I shouldn’t go during this outbreak?

The CDC has issued its highest-level travel alerts for Italy, Iran, South Korea, and China, advising Americans to avoid traveling in these places for the moment. These are the countries with the largest known coronavirus outbreaks. On March 11, President Donald Trump issued a ban on travel from most of Europe for 30 days.

But just because a country you plan to visit isn’t on the list right now doesn’t mean it won’t be there tomorrow. The outbreak is evolving rapidly, and these advisories are likely to change in the coming days, so keep checking in with the CDC. This map and list of travel restrictions from the Council on Foreign Relations is another good resource.

As Nuzzo told Vox: “I’m more concerned about the unpredictability of the [outbreak] response at this point. It would not be fun to go to China and get stuck there somehow. And coming back, you’ll be subject to additional screening” or quarantines.

What if you decide to travel and you’re seated near someone who is coughing or sneezing? That’s not very reassuring, but it’s not time to panic, either. “The risk of acquiring a respiratory infection through air travel is still extraordinarily low,” Bogoch, who studies how air travel influences the dynamics of outbreaks — including the new coronavirus infection.

The risk does go up if you happen to be seated within six feet of a person with a respiratory infection. But even there, simple proximity doesn’t necessarily mean you’ll catch anything. Instead, the more infectious the person is, and the longer you sit near them, the higher your risk. If you’re not near the person for very long or they’re not very infectious, the risk is lower.

Also keep in mind: The travel warnings are not entirely driven by the risk of catching this new virus. Airlines have been canceling or scaling back flights, trains have been halted, and countries have been imposing quarantines on travelers and citizens.

8) How is the world responding to this crisis?

On January 30, the WHO declared the outbreak a global public health emergency, and about a month later said it had become a pandemic.

A dramatic — and unprecedented — response played out in China, the country with the most Covid-19 cases. “China has implemented the most extensive cordon sanitaire [or quarantine] in the history of humankind,” Gostin told Vox. “They’ve restricted movements, caused fear and panic. They’ve violated human rights.” But they also managed to get more control over the outbreak, and cases are now declining.

Italy has adopted quarantine measures that are similar to China — first locking down some 16 million people in the country’s north, where the virus has been spreading, and then extending restrictions on movement to the entire country.

Some governments have so far been able to halt the spread of coronavirus within their borders, seemingly through quick action. In Taiwan, a small island close to mainland China, testing for Covid-19 began in late December, even as China was just beginning to discover cases and ramp up its response. The Taiwanese government also emphasized public education about curbing the disease’s spread. Taiwan has only reported one death from the virus, as of March 11.

In recent weeks, the US government dramatically escalated its response: issuing its highest-level travel advisories, quarantining citizens evacuated from China, and banning foreign nationals who have recently been to China from coming in, as well as travelers from Iran. On March 11, Trump announced a 30-day travel ban from most of Europe to the US (excluding the UK).

The CDC warned, on February 25, there may be a lot more to come; “disruption to everyday life might be severe.” This means Americans can expect more cancellations, quarantines, and social distancing efforts. (To read more about those, see this explainer.)

The severe measures can be explained by the fact that there’s still a lot we don’t know about this new virus and health officials are taking drastic actions. There’s also no enforceable international law governing outbreak responses, so countries can basically do what they want in response to pandemic threats without getting penalized, even if those actions are proportional or science-based, and the WHO is advising against them.

9) How might this end?

There are a few ways this outbreak could end, as Vox’s Brian Resnick explained. Perhaps public health measures — identifying cases fast, putting infected people in isolation — will slow the spread of this coronavirus. (That’s what stopped the spread of SARS in 2003.)

“If we slow it so that infections happen over 10 or 12 months instead of over one month, that’s going to make a big difference as far as how many people seriously infected, how many people may end up hospitalized, and how many they end up dying,” said Tara Smith, a Kent State University epidemiologist. “We talk about it as ‘flattening the epidemic curve’ — so that it’s not a big, sudden peak in cases, but it’s a more moderate plateau over time.”

Because this is a zoonotic disease, meaning it came from an animal, finding and eliminating that source would also help.

Or maybe a vaccine or antiviral will be invented quickly to curb a broader epidemic (though a vaccine is expected to take at least a year).

Related A simple guide to the vaccines and drugs that could fight coronavirus

The coming seasons of warmer weather could also play a role in at least slowing down the virus. “Coronaviruses are winter viruses,” Fauci said. “When the weather is warm and moist, these viruses don’t spread as well as when the weather is cold and dry.”

Covid-19 could also keep spreading at a high rate and become endemic — regularly infecting humans, like the common cold.

Either way, “it’s going to have tremendous — really negative and lasting effects — for the most vulnerable people who are either medically or economically vulnerable in our society,” Angela Rasmussen, a Columbia virologist, told Vox.

Correction March 3: A graphic in this piece previously misstated the percentage of cases in China that were not linked back to the Wuhan area. The graphic has been updated with the correct figure, 14 percent.

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