COVID-19 basics

Symptoms, spread and other essential information about the new coronavirus and COVID-19

As we continually learn more about coronavirus and COVID-19, it can help to reacquaint yourself with some basic information. For example, understanding how the virus spreads reinforces the importance of social distancing and other health-promoting behaviors. Knowing how long the virus survives on surfaces can guide how you clean your home and handle deliveries. And reviewing the common symptoms of COVID-19 can help you know if it's time to self-isolate.

What is coronavirus?

Coronaviruses are an extremely common cause of colds and other upper respiratory infections.

What is COVID-19?

COVID-19, short for "coronavirus disease 2019," is the official name given by the World Health Organization to the disease caused by this newly identified coronavirus.

How many people have COVID-19?

The numbers are changing rapidly.

The most up-to-date information is available from the World Health Organization, the US Centers for Disease Control and Prevention, and Johns Hopkins University.

It has spread so rapidly and to so many countries that the World Health Organization has declared it a pandemic (a term indicating that it has affected a large population, region, country, or continent).

Do adults younger than 65 who are otherwise healthy need to worry about COVID-19?

Yes, they do. Although the risk of serious illness or death from COVID-19 increases steadily with age, younger people can get sick enough from the disease to require hospitalization. And certain underlying medical conditions may increase the risk of serious COVID-19 for individuals of any age.

People of any age should take preventive health measures like frequent hand washing, physical distancing, and wearing a mask when going out in public, to help protect themselves and to reduce the chances of spreading the infection to others.

To what extent have younger adults been impacted by COVID-19?

According to a recent article in JAMA, between March and July 2020, there were almost 12,000 excess deaths in people ages 25 to 44. (Excess deaths refers to the gap between actual deaths and the expected number of death based on historical norms.) Though not all of the excess deaths were due to COVID-19, many were.

It's true that younger adults are less likely than older adults to die of COVID-19: Adults in the 25 to 44 age range account for less than 3% of COVID deaths, compared to 80% for people older than 65.

But younger people can get sick enough from the disease to require hospitalization or to die. And they may be among the long haulers — people who continue to experience fatigue, brain fog, shortness of breath, or other symptoms weeks and months after their illness.

And as is true in other age groups, COVID illness and death has a disproportionate impact on younger adults of color.

Because healthy younger adults are at lower risk than other populations, they are likely to be among the last to be vaccinated. That means it is even more important to continue wearing masks, maintaining physical distance, and avoid gathering in groups.

What are the symptoms of COVID-19?

Some people infected with the virus have no symptoms. When the virus does cause symptoms, common ones include fever, body ache, dry cough, fatigue, chills, headache, sore throat, loss of appetite, and loss of smell. In some people, COVID-19 causes more severe symptoms like high fever, severe cough, and shortness of breath, which often indicates pneumonia.

People with COVID-19 are also experiencing neurological symptoms, gastrointestinal (GI) symptoms, or both. These may occur with or without respiratory symptoms.

For example, COVID-19 affects brain function in some people. Specific neurological symptoms seen in people with COVID-19 include loss of smell, inability to taste, muscle weakness, tingling or numbness in the hands and feet, dizziness, confusion, delirium, seizures, and stroke.

In addition, some people have gastrointestinal (GI) symptoms, such as loss of appetite, nausea, vomiting, diarrhea, and abdominal pain or discomfort associated with COVID-19. These symptoms might start before other symptoms such as fever, body ache, and cough. The virus that causes COVID-19 has also been detected in stool, which reinforces the importance of hand washing after every visit to the bathroom and regularly disinfecting bathroom fixtures.

Why do some people get very sick from COVID-19 while others do not?

One of the most perplexing aspects of coronavirus is why it strikes people so differently. Why do some people sail through without a symptom, while others — even some who are otherwise healthy and relatively young — get extremely sick or even die? It may have to do with interferons.

New research suggests that up to 14% of people who develop severe COVID-19 have an inadequate interferon response. In some people, this happens because their own antibodies mistakenly attack and neutralize their interferons. Others have a genetic mutation that prevents their body from producing enough of a certain type of interferon.

Interferons are an important component of innate immunity, the quick, nonspecific immune defense the body mounts within minutes of infection to rid the body of invaders. Interferons help protect the body in a number of ways: they signal nearby cells to guard themselves against invasion; they signal infected cells to die; and they activate the adaptive immune system to mount a specific, long-term antibody response. An inadequate interferon response could help explain why some people — especially some young people without underlying conditions — get so much sicker than others their age.

Interferon treatments do exist to treat other illnesses. And interferon inhalers were given to healthcare workers in China to help prevent infection. But treatments come with their own risks, and questions about dose, timing, and type of interferon would need to be resolved before interferon therapy could be safely used for COVID-19.

Another important reason for differences in severity of COVID-19 illness is also related to the immune system. If the immune system doesn't turn off once the virus is controlled, it can go into overdrive. The result: an intense and widespread inflammatory response damaging tissues throughout the body. This is often referred to as cytokine storm.

Can COVID-19 symptoms worsen rapidly after several days of illness?

Common symptoms of COVID-19 include fever, dry cough, fatigue, loss of appetite, loss of smell, and body ache. In some people, COVID-19 causes more severe symptoms like high fever, severe cough, and shortness of breath, which often indicates pneumonia.

A person may have mild symptoms for about one week, then worsen rapidly. Let your doctor know if your symptoms quickly worsen over a short period of time. Also call the doctor right away if you or a loved one with COVID-19 experience any of the following emergency symptoms: trouble breathing, persistent pain or pressure in the chest, confusion or inability to arouse the person, or bluish lips or face.

What are cytokine storms and what do they have to do with COVID-19?

A cytokine storm is an overreaction of the body's immune system. In some people with COVID-19, the immune system releases immune messengers, called cytokines, into the bloodstream out of proportion to the threat or long after the virus is no longer a threat.

When this happens, the immune system attacks the body's own tissues, potentially causing significant harm. A cytokine storm triggers an exaggerated inflammatory response that may damage the liver, blood vessels, kidneys, and lungs, and increase formation of blood clots throughout the body. Ultimately, the cytokine storm may cause more harm than the coronavirus itself.

A simple blood test can help determine whether someone with COVID-19 may be experiencing a cytokine storm. Trials in countries around the world are investigating whether drugs that have been used to treat cytokine storms in people with other, non-COVID conditions could be effective in people with COVID-19.

One of the symptoms of COVID-19 is shortness of breath. What does that mean?

Shortness of breath refers to unexpectedly feeling out of breath, or winded. But when should you worry about shortness of breath? There are many examples of temporary shortness of breath that are not worrisome. For example, if you feel very anxious, it's common to get short of breath and then it goes away when you calm down.

However, if you find that you are ever breathing harder or having trouble getting air each time you exert yourself, you always need to call your doctor. That was true before we had the recent outbreak of COVID-19, and it will still be true after it is over.

Meanwhile, it's important to remember that if shortness of breath is your only symptom, without a cough or fever, something other than COVID-19 is the likely problem.

Does COVID-19 cause strokes? What about blood clots in other parts of the body?

Strokes occur when the brain's blood supply is interrupted, usually by a blood clot. Recently, there have been reports of a greater-than-expected number of younger patients being hospitalized for, and sometimes dying from, serious strokes. These strokes are happening in patients who test positive for coronavirus but who do not have any traditional risk factors for stroke. They tend to have no COVID-19 symptoms, or only mild symptoms. The type of stroke occurring in these patients typically occurs in much older patients.

COVID-related strokes occur because of a bodywide increase in blood clot formation, which can damage any organ, not just the brain. A blood clot in the lungs is called pulmonary embolism and can cause shortness of breath, chest pain, or death; a blood clot in or near the heart can cause a heart attack; and blood clots in the kidneys can cause kidney damage requiring dialysis.

We don't yet know if the coronavirus itself stimulates blood clots to form, or if they are a result of an overactive immune response to the virus.

Can COVID-19 affect brain function?

COVID-19 does appear to affect brain function in some people. Specific neurological symptoms seen in people with COVID-19 include loss of smell, inability to taste, muscle weakness, tingling or numbness in the hands and feet, dizziness, confusion, delirium, seizures, and stroke.

One study that looked at 214 people with moderate to severe COVID-19 in Wuhan, China found that about one-third of those patients had one or more neurological symptoms. Neurological symptoms were more common in people with more severe disease.

Neurological symptoms have also been seen in COVID-19 patients in the US and around the world. Some people with neurological symptoms tested positive for COVID-19 but did not have any respiratory symptoms like coughing or difficulty breathing; others experienced both neurological and respiratory symptoms.

Experts do not know how the coronavirus causes neurological symptoms. They may be a direct result of infection or an indirect consequence of inflammation or altered oxygen and carbon dioxide levels caused by the virus.

The CDC has added "new confusion or inability to rouse" to its list of emergency warning signs that should prompt you to get immediate medical attention.

Is a lost sense of smell a symptom of COVID-19? What should I do if I lose my sense of smell?

Increasing evidence suggests that a lost sense of smell, known medically as anosmia, may be a symptom of COVID-19. This is not surprising, because viral infections are a leading cause of loss of sense of smell, and COVID-19 is a caused by a virus. Still, loss of smell might help doctors identify people who do not have other symptoms, but who might be infected with the COVID-19 virus — and who might be unwittingly infecting others.

In addition to COVID-19, loss of smell can also result from allergies as well as other viruses, including rhinoviruses that cause the common cold. So anosmia alone does not mean you have COVID-19. Studies are being done to get more definitive answers about how common anosmia is in people with COVID-19, at what point after infection loss of smell occurs, and how to distinguish loss of smell caused by COVID-19 from loss of smell caused by allergies, other viruses, or other causes altogether.

Until we know more, tell your doctor right away if you find yourself newly unable to smell. He or she may prompt you to get tested and to self-isolate.

How long is it between when a person is exposed to the virus and when they start showing symptoms?

Recently published research found that on average, the time from exposure to symptom onset (known as the incubation period) is about five to six days. However, studies have shown that symptoms could appear as soon as three days after exposure to as long as 13 days later. These findings continue to support the CDC recommendation of self-quarantine and monitoring of symptoms for 7 to 14 days post exposure.

How does coronavirus spread?

The coronavirus is thought to spread mainly from person to person. This can happen between people who are in close contact with one another. Droplets that are produced when an infected person coughs or sneezes may land in the mouths or noses of people who are nearby, or possibly be inhaled into their lungs.

A person infected with coronavirus — even one with no symptoms — may emit aerosols when they talk or breathe. Aerosols are infectious viral particles that can float or drift around in the air for up to three hours. Another person can breathe in these aerosols and become infected with the coronavirus. This is why everyone should cover their nose and mouth when they go out in public.

Coronavirus can also spread from contact with infected surfaces or objects. For example, a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes.

The virus may be shed in saliva, semen, and feces; whether it is shed in vaginal fluids isn't known. Kissing can transmit the virus. Transmission of the virus through feces, or during vaginal or anal intercourse or oral sex, appears to be extremely unlikely at this time.

What does the CDC's new definition of "close contacts" mean for me?

The CDC has expanded how it defines close contacts of someone with COVID-19. Until this point, the CDC had defined a close contact as someone who spent 15 or more consecutive minutes within six feet of someone with COVID-19. According to the new definition, a close contact is someone who spends 15 minutes or more within six feet of a person with COVID-19 over a period of 24 hours.

Close contacts are at increased risk of infection. When a person tests positive for COVID-19, contact tracers may identify their close contacts and urge them to quarantine to prevent further spread. Based on the new definition, more people will now be considered close contacts.

Many factors can affect the chances that infection will spread from one person to another. These factors include whether or one or both people are wearing masks, whether the infected person is coughing or showing other symptoms, and whether the encounter occurred indoors or outdoors. Though the "15 minutes within six feet rule" is a helpful guideline, it's always best to minimize close interactions with people who are not members of your household.

The CDC's new definition was influenced by a case described in the CDC's Morbidity and Mortality Weekly Report in which a correctional officer in Vermont is believed to have been infected after being within six feet for 17 non-consecutive minutes of six asymptomatic individuals, all of whom later tested positive for COVID-19.

Has a mutation made it easier for the COVID-19 virus to spread?

Like other viruses, the coronavirus responsible for COVID-19 — SARS-CoV-2 — cannot survive without a living cell in which to reproduce. Once it enters human cells, SARS-CoV-2 churns out copies of itself, which go on to infect other cells. Sometimes, a mistake is made when the virus is replicating. This is called a mutation.

Mutations have led to two new coronavirus variants. One, called B.1.1.7, was first detected in the United Kingdom. The other, called B.1.351, originated in South Africa. Both variants have now been detected in countries around the globe.

Both variants contain mutations on the virus's spike protein. Spike proteins on the surface of the SARS-CoV-2 virus bind to and allow the virus to enter human cells. Interestingly, both variants share a key mutation (called N501Y) on the spike protein, that allows the virus to bind more tightly to human cells. This mutation makes the new variants more contagious than previous SARS-CoV-2 variants. But they do not appear to be deadlier than other variants.

The emergence of these highly transmissible variants is yet another reason why mask wearing, physical distancing, and avoiding crowds continues to be as important as ever.

Can people without symptoms spread the virus to others?

"Without symptoms" can refer to two groups of people: those who eventually do have symptoms (pre-symptomatic) and those who never go on to have symptoms (asymptomatic). During this pandemic, we have seen that people without symptoms can spread the coronavirus infection to others.

A person with COVID-19 may be contagious 48 hours before starting to experience symptoms. In fact, people without symptoms may be more likely to spread the illness, because they are unlikely to be isolating and may not adopt behaviors designed to prevent spread.

But what about people who never go on to develop symptoms? A study published in JAMA Network Open found that almost one out of every four infections may be transmitted by individuals with asymptomatic infections.

This study provides yet another reason to wear face masks and observe physical distancing. Both measures can help reduce the risk that someone who does not have symptoms will infect others.

Are kids any more or less likely than adults to spread coronavirus?

Most children who become infected with the COVID-19 virus have no symptoms, or they have milder symptoms such as low-grade fever, fatigue, and cough. Early studies suggested that children do not contribute much to the spread of coronavirus. But more recent studies raise concerns that children could be capable of spreading the infection.

Though the recent studies varied in their methods, their findings were similar: infected children had as much, or more, coronavirus in their upper respiratory tracts as infected adults.

The amount of virus found in children — their viral load — was not correlated with the severity of their symptoms. In other words, more virus did not mean more severe symptoms.

Finding high amounts of viral genetic material — these studies measured viral RNA, not live virus — in kids does not prove that children are infectious. However, the presence of high viral loads in infected children does increase the concern that children, even those without symptoms, could readily spread the infection to others.

How could contact tracing help slow the spread of COVID-19?

Anyone who comes into close contact with someone who has COVID-19 is at increased risk of becoming infected themselves, and of potentially infecting others. Contact tracing can help prevent further transmission of the virus by quickly identifying and informing people who may be infected and contagious, so they can take steps to not infect others.

Contact tracing begins with identifying everyone that a person recently diagnosed with COVID-19 has been in contact with since they became contagious. In the case of COVID-19, a person may be contagious 48 to 72 hours before they started to experience symptoms.

The contacts are notified about their exposure. They may be told what symptoms to look out for, advised to isolate themselves for a period of time, and to seek medical attention as needed if they start to experience symptoms.

How deadly is COVID-19?

The answer depends on whether you're looking at the fatality rate (the risk of death among those who are infected) or the total number of deaths.

Regarding the fatality rate, it appears that the risk of death with the pandemic coronavirus infection (commonly estimated at about 1%) is far less than it was for SARS (approximately 11%) and MERS (about 35%), but will likely be higher than the risk from seasonal flu (which averages about 0.1%). We will have a more accurate estimate of fatality rate for this coronavirus infection once testing becomes more routine.

What we do know so far is the risk of death very much depends on your age and your overall health. Children appear to be at very low risk of severe disease and death. Older adults and those who smoke or have chronic diseases such as diabetes or heart disease have a higher chance of developing complications like pneumonia, which could be deadly.

Can the COVID-19 virus spread through air conditioning?

We don't know for certain if the COVID-19 virus spreads through air conditioning. But we do know that when it's hot and humid, people are more likely to stay indoors, with the windows closed — giving the virus more opportunity to spread.

Coronavirus spreads through droplets that an infected person emits through coughs or sneezes and through smaller, infectious viral particles that can drift around in the air for several hours. Outdoors, air currents can scatter and dilute the virus, making transmission less likely. You're more likely to inhale the virus indoors, with the windows closed, whether or not you have the air conditioning on.

If you must be indoors with anyone outside of your household, increase air circulation by keeping the windows open as much as possible.

How long can the coronavirus stay airborne? I have read different estimates.

A study done by National Institute of Allergy and Infectious Diseases' Laboratory of Virology in the Division of Intramural Research in Hamilton, Montana helps to answer this question. The researchers used a nebulizer to blow coronaviruses into the air. They found that infectious viruses could remain in the air for up to three hours. The results of the study were published in the New England Journal of Medicine on March 17, 2020.

Can I catch the coronavirus by eating food handled or prepared by others?

The new coronavirus is a respiratory virus known to spread by upper respiratory secretions, including airborne droplets after coughing or sneezing. The virus that causes COVID-19 has also been detected in the stool of certain people. So we currently cannot rule out the possibility of the infection being transmitted through food by an infected person who has not thoroughly washed their hands. In the case of hot food, the virus would likely be killed by cooking. This may not be the case with uncooked foods like salads or sandwiches.

Should I get a flu shot?

While the flu shot won't protect you from developing COVID-19, it's still a good idea. Most people older than six months can and should get the flu vaccine. Doing so reduces the chances of getting seasonal flu. Even if the vaccine doesn't prevent you from getting the flu, it can decrease the chance of severe symptoms. But again, the flu vaccine will not protect you against this coronavirus.

Is it safe to use steroids to control allergy and asthma symptoms during the COVID-19 pandemic?

Yes, it is safe to use corticosteroid nasal sprays to control nasal allergies or inhaled corticosteroids to control asthma symptoms during the COVID-19 pandemic.

The American College of Allergy, Asthma and Immunology (ACAAI) recently issued a statement emphasizing the importance of controlling allergy and asthma symptoms during the pandemic. They said there is no evidence that intranasal or inhaled corticosteroids increase the risk of getting the COVID-19 infection or lead to a worse outcome if you do get infected.

The ACAAI statement was a response to concerns over reports warning against the use of systemic steroids to treat hospitalized COVID-19 patients with specific respiratory complications. However, those reports did not refer to healthy individuals using corticosteroid nasal sprays or inhalers to manage allergies or asthma.

Blog posts

Podcasts

Thoughts on COVID-19 during this year's flu season (recorded 10/9/2020)

With the COVID-19 pandemic still ongoing, and the annual flu season fast approaching, what can people expect when these two illnesses collide? Are we at greater risk for getting either virus? And could this encounter change how we approach health care now and in the future? Matthew Solan, executive editor of the Harvard Men's Health Watch, talks to Dr. Amy Sherman, an infectious disease expert with Harvard's Brigham and Women's Hospital, about what we may expect when COVID and the flu season meet. To learn more check out our Harvard Medical School Guide, COVID-19, Flu and Colds.

Coronavirus Update: We're facing the start of a second wave (recorded 6/11/2020)

Dr. Ashish K. Jha, head of the Harvard Global Health Institute, offers information on where we are where we're going with the COVID-19 outbreak. Some take-aways:

  • Communications missteps by the WHO regarding asymptomatic transmission have been quickly corrected. Yes, you can catch COVID-19 from people who are not showing symptoms.
  • A second wave has begun, particularly in the south and Midwest. And calculations show we'll reach more than 200,000 COVID-19 related deaths by September.
  • Jha offers advice for parents, teachers and administrators on workable back-to-school scenarios.
  • We know you don't want to hear it, but COVID-19 will be a fact of global life for the rest of the year until a vaccine becomes widely available.

A Harvard infectious diseases doctor looks at COVID-19 (recorded 3/3/20)

Dr. Todd Ellerin is on the front lines of infectious disease containment and mitigation as the director of infectious diseases at South Shore Health in Weymouth, Massachusetts. He's an instructor at Harvard-affiliated Brigham and Women's Hospital. We spoke to him this week to get an update on the rapidly developing story surrounding the coronavirus Covid-19.

Coronavirus status report: Harvard public health expert Dr. Ashish K. Jha fills us in on where we are headed (recorded 3/19/20)

The COVID-19 outbreak has caused markets to collapse and worldwide health systems to become overwhelmed. When there's a global pandemic, it's nice to hear from the steady, transparent and yes even reassuring voice of experts on the front lines. We spoke to Dr. Ashish K. Jha, faculty director of the Harvard Global Health Institute. Dr. Jha's recent appearance on the PBS Newshour caused reverberations throughout the federal and state response system. Here's his update.

For more information on coronavirus and COVID-19, see the Harvard Health Publishing Coronavirus Resource Center.

Image: gemphotography/Getty Images

Disclaimer:
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.