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The world learned about a new coronavirus 5 months ago. Here's what we now know about COVID-19.

The world has learned a great deal about the disease that has killed hundreds of thousands of people around the world.
Image: The Novel Coronavirus SARS-CoV-2, yellow, emerging from the surface of cells, pink, cultured in the lab. Also known as 2019-nCoV, the virus causes COVID-19.
A micrograph shows the coronavirus, in yellow, emerging from the surface of cells, in pink.NIAID-RML via / AP

Since the new coronavirus was first reported in China in late December, the world has learned a great deal about the disease it causes, COVID-19, that has killed hundreds of thousands of people around the world.

Initial assumptions about the virus and COVID-19 have been overturned as case counts and deaths increase around the world. Doctors know now that the coronavirus spreads easily from person to person, it can be spread by people who don't have any symptoms at all and children can also contract the illness.

COVID-19 has only been here for several months, and there is much more to learn about the pandemic disease. Here's what we know so far.

Full coverage of the coronavirus outbreak

What is a coronavirus?

Coronaviruses are a group of viruses that can cause a range of symptoms including a runny nose, cough, sore throat and fever. Some are mild, such as the common cold, while others are more likely to lead to pneumonia. They're usually spread through direct contact with an infected person.

The coronavirus gets its name from the crown-like spikes on its surface, according to the Centers for Disease Control and Prevention. ("Corona" is Latin for "crown.") Including the virus that causes COVID-19, there are a total of seven coronaviruses that can infect humans, the CDC reported. Other well-known coronaviruses include those that cause SARS and MERS.

COVID-19 stands for “coronavirus disease 2019,” the year it was discovered.

What are the symptoms of COVID-19?

According to the CDC, key symptoms to watch for include:

  • Fever
  • Cough
  • Shortness of breath or difficulty breathing
  • Chills
  • Muscle pain
  • Sore throat
  • Loss of taste or smell

Gastrointestinal symptoms — including nausea, diarrhea and vomiting — may also occur but are less common.

Up to 80 percent of people who become infected don’t need to be hospitalized and may not even know they're sick. But in severe cases, the illness can cause pneumonia, kidney damage and death, according to the World Health Organization. Other complications, including blood clots, strokes and neurological problems, have also been reported.

For some people — including those who were not sick enough to be hospitalized — symptoms including fever and fatigue can linger for weeks. Some people have experienced such long-lasting illness that they've turned to social media for help when they couldn't get answers from their doctors.

Who is most at risk?

By far, older adults — especially people over age 80 with underlying medical conditions, such as heart disease, diabetes or lung diseases — are most vulnerable to complications of the coronavirus.

Younger people, however, are still susceptible to severe complications from COVID-19. A CDC report from March found that in a sampling of hospitalized patients, more than half were under 65, and 20 percent were in their 20s, 30s or early 40s.

Underlying medical conditions are also a factor: People with obesity, diabetes and high blood pressure are at greater risk for complications from the coronavirus, according to a large study of hospitalized patients.

Are children getting the coronavirus?

COVID-19 cases in children remain rare, and most of the time, the illness is mild. It’s unclear why most children appear to be spared.

In rare cases, however, children with COVID-19 can become very ill, and several deaths have been reported. Many that do get very sick have underlying medical conditions.

The coronavirus is also being linked to a rare and potentially deadly inflammatory condition that can occur in children several weeks after they were infected with the virus. The condition, officially called multisystem inflammatory syndrome in children, or MIS-C, has been reported in several states in the U.S.

The condition resembles other inflammatory illnesses including Kawasaki disease and toxic shock syndrome. Symptoms include a fever of at least 100.4 degrees, evidence of inflammation in the body and hospitalization with problems in at least two organs, plus a positive COVID-19 test or exposure to a positive individual.

How does the coronavirus spread?

The coronavirus spreads through respiratory droplets when a sick person coughs, sneezes or speaks. People within 6 feet of an infected individual are most at risk for inhaling these droplets.

The main way the virus spreads is through close contact with other people. It's possible that the virus can also spread through contact with contaminated surfaces, but according to the CDC, this is not thought to be the main mode of transmission. Still, it's recommended that people regularly clean and disinfect surfaces.

How long does it take for someone to get sick?

The coronavirus's incubation period — meaning the time it takes from a person being infected with the virus to when they start showing symptoms — appears to be anywhere from two to 14 days. Though, the average amount of time it takes a person to show symptoms is about five days, according to the World Health Organization.

Can I spread the coronavirus if I don’t have symptoms?

Yes, a person can spread the coronavirus even when they do not have symptoms. Sometimes, this type of transmission is referred to as “presymptomatic spread,” meaning that a person will go on to develop symptoms. In other instances, known as “asymptomatic spread,” where an individual never develops symptoms but can still be contagious. Asymptomatic spread could account for up to a quarter of transmissions of the virus, and according to the CDC, an estimated 35 percent of people infected are asymptomatic.

A study in the journal Nature, published in April, found that people with minor complaints — slight cough, headache, low-grade fever — are most contagious at the earliest stages of their illness, either right before their symptoms begin or within the first few days.

If I get the coronavirus and recover, am I immune?

It’s too early to say whether catching the coronavirus gives you immunity against catching the virus again. Immunity depends on whether, after people get sick, they develop the antibodies needed to fight off the virus — and how long these antibodies last in the body.

Many researchers hypothesize that people will develop immunity to the virus, at least for some period of time, as was the case with two other coronaviruses, SARS and MERS. Evidence from one study using rhesus macaques — monkeys that share a majority of their genes with humans — have shown that after a coronavirus infection, the macaques developed antibodies that protected them from getting sick again.

Evidence so far from antibody testing suggests people do develop antibodies after a coronavirus infection. But it’s still unclear whether these antibodies are protective, and only time will tell how long they last in the body.

Can I get the coronavirus outside?

There's a growing consensus in the scientific community that the risk of getting the coronavirus outdoors is low. Experts generally agree that it’s safe to spend time outdoors, provided that people follow social distancing guidelines and practice good hygiene.

Scientists think most coronavirus cases resulted from close contact with an infected person, particularly when in an enclosed space, such as in the home.

How can I protect myself from the coronavirus?

One of the simplest prevention measures a person can take is proper hand-washing.

The CDC recommends washing hands with soap and water before eating; after using the bathroom, blowing your nose, coughing or sneezing; and before and after caring for a sick friend or a family member.

The most effective way to clean hands is to wet them with clean water, then apply soap and scrub for at least 20 seconds, before rinsing and drying with a clean towel.

Soap helps lift germs from the surface of the skin, but it's the scrubbing that gets germs off hands. Hand sanitizer is a good alternative, but it must have at least 60 percent alcohol to be effective, according to the CDC.

What else can I do besides washing my hands?

Perhaps the best way to prevent the spread of the coronavirus is to keep sick people separated from healthy people.

The concept, called social distancing, is illustrated in the myriad measures businesses, sports organizations, school systems and others have taken to cut down on large gatherings. Many public events are canceled or postponed; students and employees are encouraged to do their work from home.

Otherwise, infectious disease experts recommend staying 6 feet away from others.

Should I wear a face mask?

People may have the coronavirus but not realize they are sick. Wearing a cloth face covering over your nose and mouth helps prevent virus particles from spreading to others when you speak and breathe.

A face covering likely does not reduce your own chance of getting sick, but it helps protect others around you.

Beginning in April, the CDC recommended that individuals use cloth face coverings "in public settings where other social distancing measures are difficult to maintain," such as grocery stores and pharmacies. The guidance recommends people use fabric coverings, not surgical masks or specialized N95 masks, which should be reserved for health care providers.

Information about how to make masks at home is available online.

Is there a coronavirus vaccine?

There is currently no vaccine to prevent the coronavirus. The earliest a vaccine could be available is 2021, 12 to 18 months after scientists started vaccine development. If a vaccine is successfully produced in that time frame, it would be the fastest ever developed.

Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, told NPR "it's conceivable" that a vaccine will be ready to deploy by December 2020 or January 2021.

A number of vaccines are in development, including several that have reached clinical trials, where the vaccines are studied in humans. Moderna, a company based in Cambridge, Massachusetts, plans on starting large phase 3 trials over the summer.

At the same time, drug developers are beginning to produce large amounts of the experimental vaccines, so that if they turn out to be successful, they’ll be ready to distribute.

Is there a coronavirus treatment?

So far, one treatment, called remdesivir, has received an emergency use authorization in the U.S. for people with COVID-19 who are severely ill. Remdesivir is an antiviral drug originally developed to treat Ebola.

A study conducted by the National Institutes of Health found that hospitalized patients who received remdesivir were able to be discharged within 11 days, on average, compared to 15 days among people who received a placebo.

Still, the drug is not considered a cure, and further research is ongoing.

Other possible treatments are also being looked at in clinical trials, including anti-inflammatory drugs and so-called convalescent plasma, which is an antibody-rich blood product taken from a patient who has fully recovered from COVID-19.

In June, British researchers reported that another drug, a steroid called dexamethasone, was found to reduce deaths in the sickest COVID-19 patients.

Do disinfectants kill the coronavirus?

Yes, they can. The CDC suggests that anyone exposed to an infected patient clean all "high-touch" surfaces, such as counters, tabletops, doorknobs, bathroom fixtures, toilets, phones, keyboards, tablets and bedside tables.

Cleaning agents can include a household disinfectant with a label that says "EPA-approved," according to the CDC. A homemade version can be made, using 4 teaspoons of bleach to 1 quart of water.

Experts say that when you spray sanitizer or use sanitizing wipes, it's important to let the solution dry on the surface, rather than wiping it off.

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