11 questions about the Covid-19 coronavirus outbreak, answered

The coronavirus outbreak, centered in China, keeps evolving at a dizzying speed. With the case toll rising steeply (reaching over 82,000 on February 27), face masks flying off store shelves, and businesses, cruise ships, and entire cities upended by the virus, it’s no wonder questions and fears are swirling about Covid-19, as the disease is known.

The likelihood that we’re in a pandemic, a new disease that spreads around the world — or that we’re hurtling toward one — also seems higher than just a few weeks ago. That means more countries are likely to see a spread of the virus within their borders very soon — and that includes the US, the Centers for Disease Control and Prevention (CDC) warned on February 25.

Source: Johns Hopkins University Center for Systems Science and Engineering

“The spread in other countries has raised our level of concern and our level of expectation we’re going to have community spread here,” said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases. “It’s not a question of if this will happen, but when this will happen, and how many people in this country will have severe illnesses.”

By February 26, California announced a new Covid-19 case involving a person who had not traveled to any of the affected countries nor been in contact with anyone who had. Meanwhile, outbreaks have been surging outside of China, as far and wide as 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.

Coronaviruses owe their name to the crown-like projections, visible here under a microscope, that encircle the capsid.
Universal Images Group via Getty Images

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 the leading hypothesis is that bats were once again the original source: They spread the virus to pangolins, and pangolins to humans.

2) What are the symptoms?

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 the others lead to milder symptoms, like a common cold.

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:

Christina Animashaun/Vox

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, where most of the 2,012 deaths have occurred. And for reasons no one yet understands, the case fatality rate has been lower outside of mainland China.

Christina Animashaun/Vox

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 seem more like seasonal flu than like SARS. 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.

As for symptoms: According to the CDC, most patients start with a fever, cough, and shortness of breath.

A report, published in The Lancet, provided more detailed information. It looked at a subset of the first 41 patients with confirmed Covid-19 in Wuhan, China, the mainland Chinese city of 11 million where the outbreak is believed to have started.

Christina Animashaun/Vox

The most common symptoms were fever, cough, muscle pain, and fatigue; less common were headache, diarrhea, and coughing up mucus or blood. All had pneumonia and lung abnormalities on CT scans. As for the disease severity, 32 percent were admitted to an ICU, and 15 percent died. By January 22, most (68 percent) of the patients had been discharged from the hospital.

3) How do coronaviruses spread?

We don’t yet know how 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 could spread through poop — known as the “fecal-oral” route of disease transmission. Researchers are on the lookout for potential airborne transmission, too.

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

The CDC has issued its highest-level travel alerts for South Korea and China, advising Americans to avoid traveling there for the moment. The two countries currently have the most coronavirus cases: more than 78,000 in mainland China, and 1,500 in South Korea.

As of this week, the CDC is also warning travelers to Italy, Iran, and Japan to “practice enhanced precautions,” since these are the countries with the next-highest burden of illness.

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.

A tourist wearing a respiratory mask at the Trevi Fountain in downtown Rome on January 31, 2020. The Italian government declared a state of emergency to prevent the spread of the new coronavirus after two cases were confirmed in Rome.
Filippo Monteforte/AFP via Getty Images

And 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 sometimes arbitrary quarantines on travelers and citizens.

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,” said Isaac Bogoch, a professor at the University of Toronto 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.

5) I’m still worried about the new coronavirus. 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.

People wear medical masks as a precaution against coronavirus, walking around New York, on January 30, 2020.
Tayfun Coskun/Anadolu Agency via Getty Images

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.)

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 Messonnier said, is “wash your hands, cover your cough, take care of yourself, and keep alert to the information that we’re providing.”

6) What about the cases of people spreading the virus before they show symptoms? Isn’t that worrisome?

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.

Javier Zarracina and Christina Animashaun/Vox

But “we still don’t know to what extent people without symptoms can infect,” Nuzzo cautioned. And, as Bogoch 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.

7) Is this going to become a deadly pandemic?

The CDC and WHO are still calling this an outbreak. But with case counts now surging in numerous countries besides China, health experts told Vox we’re on the brink of a pandemic — or we’re already in one. That means containing the virus — fully halting its spread — may no longer be possible.

“I don’t think the answer is shutting down the world to stop this virus. It’s already out,” said Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy.

“We are at a turning point in the Covid-19 epidemic,” said Lawrence Gostin, a global health law professor at Georgetown University. “We must prepare for the foreseeable possibility, even probability, that Covid-19 may soon become a pandemic affecting countries on virtually all continents.”

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 a Covid-19 pandemic would look like — mostly because we don’t yet know precisely how lethal this disease is.

If you take the current number of deaths and divide it by the number of known cases, “the case fatality is 2 percent — and it’s gone down from 3 percent in the early days,” said the University of Michigan’s Howard Markel, who studies outbreaks. “And if it goes really, really low, we’ll probably say — like we did in Mexico in 2009 with [H1N1] swine flu — that it’s something very similar, if not less deadly [than] regular seasonal flu.”

Right now, most of the testing has focused on travelers from China and people with links to travelers from China. Once the testing is broadened and more mild cases are discovered, this virus could look a lot less deadly.

“We live [with] and tolerate a whole lot of respiratory viruses,” Nuzzo said, “some of which are even more transmissible than the estimates people have come out with for this one — but they don’t make the headlines.”

8) Is my city at risk of an outbreak?

Some of the best research on that question comes from researchers at the University of Oxford, University of Toronto, and the London School of Medicine and Tropical Hygiene. They published studies a few weeks ago on the places most vulnerable to novel coronavirus infections. The big takeaway then was that cities in East Asia and Southeast Asia were most at immediate risk.

Here are 15 of the top destinations where they predicted we’d see outbreaks next (also pay attention to the IDVI, or Infectious Disease Vulnerability Index, number. It’s a measure of a country’s ability to manage infectious disease. Scores closer to zero mean they’re less prepared.)

Oxford Journal of Travel Medicine

Note that cities in Japan, Singapore, and South Korea were among the places that topped the list — and as we’re seeing now, some of the biggest outbreaks outside of China are playing out in these countries.

Iran and Italy are also on the list, and over the past week, large outbreaks have emerged in these countries, too.

With the scope of this outbreak changing rapidly, the researchers just updated their models in a yet-to-be-published study focused on how the coronavirus disease will likely spread from Iran. They found that Iran probably has thousands more cases within its borders than we currently know. And they predict that we can expect outbreaks with links back to Iran in Turkey, the United Arab Emirates, Iraq, Qatar, and Georgia, among other countries. In Europe, they predict Germany, France, and Italy are also at higher risk of imported cases from Iran.

This is a long-winded way of saying these places may be at immediate risk, according to some of the best guesses available.

9) What might happen next?

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 impossible.

This means we’re likely to see more sickness and death not only in China but also in other countries, as cases grow from one-off travelers or small clusters to full-blown outbreaks.

In this scenario, Tony Fauci, the head of the National Institute of Allergy and Infectious Diseases, said, “you don’t try to control [the virus] because it’s already everywhere.”

Two women wear face masks on January 31, 2020, in Newcastle upon Tyne, England.
Ian Forsyth/Getty Images

Health officials will begin to move into a new mitigation phase in their response strategy. This involves a focus on reducing the spread and caring for the very sick. So hospitals need to be ready with Covid-19 protocols, health care workers need to be protected with access to protective equipment such as face masks, and countries need plans in place for maintaining supply chains and carrying on with travel and trade.

But again, even if this virus moves around the world, it may not do much harm. In the best-case scenario, 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.

10) How is the world responding to this crisis?

On January 30, the WHO declared the outbreak a global public health emergency. Though it advised countries not to put in place travel or trade restrictions against China, several — including Russia and Singapore — sealed their borders, and even more have followed with the same move since.

Meanwhile, the US government dramatically escalated its response — issuing its highest-level travel advisory, quarantining citizens evacuated from China, and temporarily banning foreign nationals who have recently been to the East Asian country from coming in.

By February 25, CDC added travel advisories for South Korea, Italy, Iran, and Japan and warned that further Covid-19 spread in the US means “disruption to everyday life might be severe.”

The severe measures can be explained by the fact that there’s still a lot we don’t know about this new virus — and that we have 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 the WHO advises against whatever actions they’re taking.

That appears to be the case in China, where the most dramatic — and unprecedented — response is currently playing out. “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.”

Authorities there have also censored information and silenced the whistleblowers who tried to sound the alarm sooner than Chinese authorities were willing, and kicked out foreign journalists critical of China’s outbreak response. But again, because of the weakness of global health law, the international community has remained mostly silent about these actions.

11) 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 stop the spread of this coronavirus. (That’s what stopped the spread of SARS in 2003.) Again, probably because of the contagiousness of this respiratory virus, this approach appears inadequate.

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 that’ll take time).

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.”

Finally, there’s the possibility the virus will simply die out. “Disease outbreaks are a bit like fires,” Resnick wrote. “The virus is the flame. Susceptible people are the fuel. Eventually, a fire burns itself out if it runs out of kindling. A virus outbreak will end when it stops finding susceptible people to infect.”

Correction 3/2: 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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Covid-19 may be on the brink of becoming a pandemic. Vox’s Julia Belluz explains what that p-word means and Brian Resnick breaks down what an outbreak response might look like in the United States.

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