A computer illustration of coronavirus particles.
A computer illustration of coronavirus particles.
  • There are more confirmed cases of COVID-19 in the U.S. than in any other country. There have been at least 1 million cases and at least 63,000 deaths in the U.S.
  • Many Americans have been ordered or encouraged by their local governments to stay home as much as possible. Some states have begun lifting lockdown orders and allowing businesses to reopen.
  • There have been more than 3.2 million cases and at least 233,000 deaths around the world.
  • The State Department says U.S. travelers should avoid all travel abroad. The CDC says residents of New York, New Jersey, and Connecticut should avoid non-essential domestic travel.
  • The virus causes respiratory problems that can range from a mild cough to severe pneumonia.
  • This article is being updated as the situation changes. 

The coronavirus pandemic has upended life in much of the world. Cities, states, and countries have ushered in a new era of social distancing, with many enacting rules and guidelines to keep citizens in their homes as much as possible.

The unprecedented efforts are designed to slow the spread of a previously unknown virus, which has already infected at least 3.2 million people around the world and led to more than 233,000 deaths. Thousands of new cases are still reported each day, even as some areas have begun easing restrictions.

COVID-19, the disease caused by the virus, leads to respiratory symptoms that range from mild (coughing, fever) to severe (pneumonia, trouble breathing). The worst cases can be fatal, especially in older adults and people with underlying health conditions.

Though the virus first emerged in Wuhan, China in the fall of 2019, there have now been more confirmed cases of COVID-19 in the U.S. than in any other country in the world.

The first U.S. case was reported on Jan. 20, in a traveler who had spent time in Wuhan. For weeks, the only cases reported in the U.S. were in travelers or their close contacts. But a little more than a month after that first imported case, the country’s first case of unknown origin appeared in California—just a few days after the Centers for Disease Control and Prevention warned that Americans should expect to see the disease spread within our borders.

As the U.S. slowly ramped up its testing capacity, new cases began popping up across the country. Now there have been at least 1 million reported cases in the U.S., spread out across all 50 states, according to a Johns Hopkins University tally. At least 304,000 of those cases are in New York state. Many more cases may be unreported, experts say. There have been at least 63,000 deaths in the U.S.

More on the Coronavirus

It took just a few short months for the virus to spread from a city in China to practically every corner of the world. The World Health Organization declared the situation a public health emergency at the end of January. On March 11, the WHO said for the first time that the spread and severity of COVID-19 means it should be characterized as a pandemic. Two days later, President Trump declared a national emergency.

On March 16, Trump announced new guidelines in a bid to help slow the spread of the virus. The guidelines say Americans should work from home if possible; avoid discretionary travel, shopping trips, and social visits; avoid social gatherings in groups of more than 10; avoid eating or drinking at bars, food courts, and restaurants; and not visit nursing homes or retirement or long-term care facilities. Many states and cities went further, closing all schools and non-essential businesses. 

Alone, these measures will not be enough to stop the spread of the virus, according to Jennifer Nuzzo, Ph.D., an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security, and an associate professor at the Johns Hopkins Bloomberg School of Public Health. “Social distancing measures ... are not a cure,” Nuzzo said on an April 10 press call. “They’re a pause button, employed in an attempt to slow the growth in cases with the goal of keeping the growth below the upper limits of health care capacity.”

To move forward, said Nuzzo, the U.S. also needs to step up its capacity to test for the disease, isolate sick people, track their contacts, and monitor what’s happening at hospitals around the country. On April 16, President Trump announced new guidelines suggesting that governors in states without ongoing spread could decide to begin easing some restrictions in phases, though public health officials cautioned that this process would need to be slow, staggered, and carefully monitored.

As the federal guidelines expired on April 30, many states began lifting lockdown orders and allowing certain businesses to reopen, often with restrictions in place such as reduced capacity.

Such changes will help speed the return to a semblance of normal, but some disruption to everyday life can be expected until we have a vaccine, many experts say—a process that “is going to take a year, a year and a half at least,” said Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, at a March 3 White House briefing. 

Here’s what we know so far about the virus.

The New Coronavirus

The new pathogen is part of a large family of viruses known as coronaviruses. (Under a microscope, these viruses look like they have a crown, or corona.)

At first, the virus was referred to simply as “2019 novel coronavirus” (2019-nCoV). Its official name is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The disease caused by this new virus has another name: coronavirus disease 2019 (COVID-19).

Coronaviruses are very common in animals, and many strains affect humans, according to Thomas File, M.D., president of the Infectious Diseases Society of America (IDSA). Most known coronaviruses cause mild conditions, such as the common cold and conjunctivitis, but the new virus is not the first time a coronavirus has led to hospitalizations and deaths.

“We have seen very serious manifestations of symptoms from other novel coronaviruses such as SARS and MERS,” File said. In 2002 to 2003, an outbreak of severe acute respiratory syndrome (SARS) sickened more than 8,000 people and killed 774. Almost 10 years later, another coronavirus, known as Middle East respiratory syndrome (MERS), emerged and has since infected 2,499 people and killed 861. (Though the new coronavirus has infected many more people, the fatality rate so far has been far lower than that of either SARS or MERS.)

According to the CDC, many of the first COVID-19 cases had links to a large seafood and live animal market in Wuhan.

How Does This Coronavirus Spread?

Though the first cases of the new coronavirus seem to have spread from animals to people, the virus is now spreading from person to person “easily and sustainably,” according to the CDC.

An early analysis of the first 425 confirmed cases estimated that each infected person was spreading the virus to approximately 2.2 other people. But the authors cautioned that this is a preliminary number, that it’s subject to change, and that the goal of control measures is to drive this number down.

As a respiratory virus, the coronavirus spreads in droplets when someone coughs or sneezes, according to File at the IDSA. People can also release viral particles when they talk, sing, or exhale. That means people within 5 or 6 feet of an infected person would be the most likely to get sick—when those viral particles land on a mucous membrane, like in your eye. Such viruses can also spread when people touch a surface contaminated with infectious droplets, then touch their own nose, mouth, or eyes. 

These viruses “don’t float around on the air for days on end,” said Isaac Bogoch, M.D., an epidemiologist and associate professor of infectious diseases in the department of medicine at the University of Toronto. Some research has shown that—for shorter periods of time, and particularly in poorly ventilated areas—SARS-CoV-2 may remain in the air in tiny particles known as aerosols. But experts say someone is still most likely to get COVID-19 from a person in close proximity to you, or by touching a contaminated surface and then touching your face. According to the CDC, while transmission via contaminated surfaces is possible, it is “not thought to be the main way the virus spreads.”   

Evidence has shown that people infected with the novel coronavirus may be able to spread it to others before they seem to have symptoms, or when their symptoms are very minor.

SARS-CoV-2 is particularly tricky, because it seems to replicate both in the upper airway and deep in the lungs, according to Vineet Menachery, Ph.D., an assistant professor in the Department of Microbiology & Immunology at the University of Texas Medical Branch at Galveston. "Where these viruses replicate really dictates how they spread and how severe the disease is," he said on an April 10 press call.

Common cold viruses are so contagious because they tend to replicate in the upper airway, causing coughing and sneezing that spread disease. The first SARS and the MERS coronaviruses were so deadly because of the damage they caused while replicating deep in the lungs, but they didn't spread as much because they didn't infect the upper airway, according to Menachery. By replicating in both the upper airway and deep in the lungs, the new virus seems able to both spread easily and cause severe disease.

“We know there is virus spread before you develop symptoms, and then we know that there’s a large group—we don’t know the precise percent yet—that actually is asymptomatic or has such mild cases that they continue to spread the virus,” said Deborah L. Birx, M.D., the coronavirus response coordinator for the White House, at a March 16 press briefing.

People who get COVID-19 appear to get sick in a time frame of a couple of days to two weeks after being exposed.  

At present, there’s no reason to think the pathogen could be transmitted through food or via consumer goods. (See our story about food safety and coronavirus.) Other coronaviruses similar to the new one don’t last very long on surfaces, said the CDC, which means transmission via surfaces after days or weeks would be highly unlikely.

What Are the Symptoms?

There have been a wide range of symptoms so far, ranging from mild to severe. In most cases, people have had a fever and dry cough. In the more severe cases, people have developed serious pneumonia and shortness of breath.

Fatigue is also common, and some people experience diarrhea or nausea. Anecdotal reports suggests some people with COVID-19 say they lose their sense of smell and taste. (Read more about recognizing the symptoms of COVID-19.)

In a small percentage of cases, the disease has been fatal.  

Most people who fall ill recover within two weeks. People with more severe cases generally recover in three to six weeks.  

A study published Feb. 24 in JAMA by the Chinese Center for Disease Control and Prevention looked at 44, 672 confirmed cases of COVID-19 in China. The researchers characterized 81 percent as mild, 14 percent as severe, and 5 percent as critical. 

Scientists have also been trying to figure out what’s known as the case fatality rate—the percentage of cases in which the virus is fatal. COVID-19 appears to be deadlier than the seasonal flu, which kills about 0.1 percent of people who are infected. But beyond that, there has been a range of estimates.

In the study by the China CDC, among people with confirmed infections, 2.3 percent died; that rate was far higher in people who were 70 and older or who had chronic health conditions. 

In Wuhan, between 2 and 4 percent of reported cases have been fatal; in other parts of China, the fatality rate has been 0.7 percent, according to a WHO briefing on Feb. 24. In Italy, in late March, the case fatality rate was reported as about 7 percent, potentially in part because of that country's older population, researchers suggested.

On March 3, at a press briefing, WHO officials said that around the world, 3.4 percent of people known to have COVID-19 have died.

But there’s an important caveat to all these estimates, says Bogoch at the University of Toronto. “There’s a growing narrative of people with very mild symptoms who are not sick enough to seek care and not counted,” he said. That means we can’t accurately calculate the fatality rate. “When we’re able to account for everybody and we have the true denominator, I would not be surprised if it were less than 2 or even less than 1 percent,” he said.

That echoes what Fauci and CDC Director Robert Redfield wrote in the New England Journal of Medicine: “If one assumes that the number of asymptomatic or minimally symptomatic cases is several times as high as the number of reported cases, the case fatality rate may be considerably less than 1 percent.”

Who Is at Risk?

At first, almost all the known cases were clustered in and around Wuhan, and in people who had recently returned from the region. On Feb. 25, for the first time, more new cases were reported outside of China than inside of China. By mid-March, the cumulative number of cases outside of China exceeded the number inside of China.

Now, hotspots have developed in several U.S. and European cities, where the number of cases is growing daily and the risk of exposure may be high.

We’re still working to understand which segments of the population are most at risk of infection and complications, according to Lisa Maragakis, M.D., the hospital epidemiologist at Johns Hopkins Hospital in Baltimore and the senior director of infection prevention at the Johns Hopkins Health System. 

In general, “elderly patients and those with underlying diseases tend to do worse with any pneumonia,” said Richard Wunderink, M.D., a professor of medicine at the Northwestern University Feinberg School of Medicine in Chicago who has written about coronaviruses.

And that seems to be the pattern for COVID-19 as well. The study from the China CDC found that while the fatality rate overall was 2.3 percent, it was 8 percent among people in their 70s, 14.8 percent among people 80 and older, 10.5 percent among people with heart disease, and 7.3 percent among people with diabetes. Meanwhile, only a small number (1 percent) of confirmed cases were in children under 10; none of them were fatal.

Still, Fauci cautioned, in an interview with CNN: “The virus isn't a mathematical formula. There are going to be people who are young who are going to wind up getting seriously ill.”

According to the CDC, certain groups are at a higher risk for getting sick. That includes people in areas where the virus has been spreading within the community, healthcare workers caring for infected patients, close contacts of people with COVID-19, and travelers returning from locations where there is community spread.

The CDC has posted recommendations for schools, homes, communities, and businesses on a website that’s being updated regularly. You can also check your state health department's website for information specific to your region.

What Should Travelers Know About the Virus?

The State Department has issued a global coronavirus-related travel warning, saying U.S. citizens should avoid all travel abroad. "In countries where commercial departure options remain available, U.S. citizens who live in the United States should arrange for immediate return to the United States, unless they are prepared to remain abroad for an indefinite period," the warning says.

The CDC says all travelers should avoid cruise ship travel and says that older adults and people with underlying disease should avoid non-essential long plane trips and crowded areas.

The CDC has also issued an alert advising residents of New York, New Jersey, and Connecticut to avoid non-essential domestic travel. 

In general, travelers should remain vigilant and keep up to date with the latest advisories from the CDC, Maragakis says. The CDC does not recommend masks for travelers. 

Many international flights have been suspended or canceled. Some domestic flights have also been canceled because of reduced demand.

Airlines that have announced at least some suspensions include Air Canada, American Airlines, British Airways, Delta, Lufthansa, and United. (The airlines’ sites have more information on the specific dates of the suspensions and what to do if you have a booking. If you’ve already booked travel or are planning a trip, see our travel article for more specific advice.)

Foreign nationals who are coming from (or via) Iran, China, the United Kingdom, or a most of Europe will be denied entry to the U.S. The CDC has also advised travelers coming from many other countries where COVID-19 is spreading (see the full list here) to quarantine themselves at home for 14 days when they arrive in the U.S.

Whatever restrictions the government implements, one important line of defense is travelers themselves. People who have recently traveled to an affected area should contact health officials if they notice any symptoms of infection. The CDC is distributing hundreds of thousands of educational cards to arriving travelers so that people can be on the lookout for any symptoms that might be the new coronavirus.

In the case of the first two U.S. patients identified, both had reentered the U.S. before airport screening of those coming from Wuhan had begun. Both contacted their healthcare providers because of their symptoms and travel history.  

How Should You Protect Yourself?

Health officials have advised isolating at home as much as possible, avoiding gatherings, and—especially if you are in an at-risk group—limiting trips out in public. Local health officials in areas where COVID-19 is spreading widely may have even stricter advice.

If you're not feeling well or have been exposed to the virus, you may be advised to quarantine yourself for 14 days. This means making a plan and getting just a couple of weeks’ worth of food, soap, and other essentials—no need to hoard supplies. (For more information, see our article on what you might need.)

The CDC is now recommending that nearly everyone wear a basic cloth or fabric face covering when out in public. (Medical masks are generally in short supply and should be reserved for healthcare workers.) While a mask does not provide much protection to the wearer, it can help someone who is sick protect those around them. Since people can be contagious before they feel sick, some research suggests universal mask wearing may help curb transmission—though not all experts agree. (See our story for more on making sense of the conflicting guidance on masks.)

Measures that can also help protect you from the flu—like frequent hand-washing and avoiding sick people—can also protect you from COVID-19. For more information, see our article on how to protect yourself

What Experts Still Don't Know

“Almost every day, we’re learning things we didn’t know before,” Robert Redfield, M.D., the director of the CDC said at a late-January press conference.

We still need to learn exactly how the virus spreads from person to person and how likely people are to get sick when they’re exposed, Maragakis says.

Scientists are also working on understanding the best treatment strategies for those who do fall ill, Bogoch says.

We also need more data to calculate the mortality rate, File says.

“How many people are exposed who don’t show symptoms or who have mild symptoms? That’s hard to figure out during cold and flu season,” says Amanda McClelland, R.N., M.P.H., senior vice president of Prevent Epidemics at Resolve to Save Lives, an initiative of Vital Strategies.

The CDC describes this as a “rapidly evolving situation,” and said information will be updated as it becomes available.  

Editor’s Note: This article was originally published Jan. 23. 

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