Coronavirus Resource Center

As coronavirus spreads, many questions and some answers

The rapid spread of the virus that causes COVID-19 continues to spark alarm worldwide. Countries around the world are grappling with surges in confirmed cases, hospitalizations, and deaths. Calls for preventive measures such as social distancing and face coverings to slow the spread of coronavirus have created a new normal in many places. Health care workers and hospitals have ramped up capabilities to care for large numbers of people made seriously ill by COVID-19. Meanwhile, scientists are exploring potential treatments and clinical trials to test new therapies and vaccines are underway.

Below, you'll find answers to common questions all of us are asking. We will be adding new questions and updating answers as reliable information becomes available. Also see our podcasts featuring experts discussing coronavirus and COVID-19.

Symptoms, spread, and other essential information

What is coronavirus and how does it spread? What is COVID-19 and what are the symptoms? How long does coronavirus live on different surfaces? Take a moment to reacquaint yourself with basic information about this virus and the disease it causes.

Click here to read more about COVID-19 symptoms, spread, and other basic information.


Social distancing, hand washing, and other preventive measures

By now, many of us are taking steps to protect ourselves from infection. This likely includes frequent handwashing, regularly cleaning frequently touched surfaces, and social distancing. How do each of these measures help slow the spread of this virus, and is there anything else you can do?

Click here to read more about what you can do to protect yourself and others from coronavirus infection.


If you are at higher risk

Though no one is invulnerable, we've seen that older adults are at increased risk for severe illness or death from COVID-19. Underlying conditions, including heart disease, lung disease, and diabetes, increase risk even further in those who are older. In addition, anyone with an underlying medical condition, regardless of their age, faces increased risk of serious illness.

Click here to read more about what you can do if you are at increased risk for serious illness.


If you've been exposed, are sick, or are caring for someone with COVID-19

Despite your best efforts, you may be exposed to coronavirus and become ill with COVID-19. Or you may be in a position where you are caring for a loved one with the disease. It's important to know what to do if you find yourself in any of these situations. Stock up with medications and health supplies now, and learn the steps you can take to avoid infecting others in your household and to avoid getting sick yourself if you are caring for someone who is ill.

Click here to read more about what to do you if you have been exposed, are sick, or are caring for someone with COVID-19.


Treatments for COVID-19: What helps, what doesn't, and what's in the pipeline

While there are no specific treatments for COVID-19 at this time, there are things you can do to feel better if you become ill. In the meantime, researchers around the globe are looking at existing drugs to see if they may be effective against the virus that causes COVID-19, and are working to develop new treatments as well.

Click here to read more about measures that can help you feel better and treatments that are under investigation.


Coronavirus and kids:

So far, the vast majority of coronavirus infections have afflicted adults. And when kids are infected, they tend to have milder disease. Still, as a parent, you can't help but worry about the safety of your children. Many parents are also trying to find a balance between answering their children's questions about the pandemic and enforcing health-promoting behaviors and social distancing rules without creating an atmosphere of anxiety. Not to mention keeping kids engaged and entertained with schools closed and playdates cancelled.

Click here to read more about kids and the coronavirus outbreak.


Coping with coronavirus:

The news about coronavirus and its impact on our day-to-day lives has been unrelenting. There's reason for concern and it makes good sense to take the pandemic seriously. But it's not good for your mind or your body to be on high alert all the time. Doing so will wear you down emotionally and physically.

Click here to read more about coping with coronavirus.


New questions and answers

Who are long-haulers? And what is post-viral syndrome?

Long-haulers are people who have not fully recovered from COVID-19, weeks or even months after first experiencing symptoms. Post-viral syndrome, or post-COVID-19 syndrome, refers to the constellation of symptoms long-haulers are experiencing.

As the pandemic has worn on, it's become clear that not everyone is recovering from COVID-19 as quickly as expected. Some people continue to experience symptoms for weeks or even months. Others feel better for weeks, then relapse with old or new symptoms.

It's difficult to predict who will become a long-hauler. Many long-haulers initially had mild to moderate symptoms and did not require hospitalization. Previously healthy young adults, not just older adults with coexisting medical conditions, are also experiencing post-COVID-19 syndrome.

Symptoms of post-COVID-19 syndrome, like symptoms of COVID-19 itself, can vary widely. Some of the more common lasting symptoms include fatigue, brain fog, shortness of breath, chills, body ache, headache, joint pain, chest pain, cough, and lingering loss of taste or smell. The common thread is that long-haulers haven't returned to their pre-COVID health, and ongoing symptoms are negatively affecting their quality of life.

There's already some speculation, but no definite answers, about what is causing these ongoing symptoms. Some researchers suspect that SARS-CoV-2 infection triggers long-lasting changes in the immune system. Others propose that it triggers autonomic nervous system dysregulation, which can impact heart rate, blood pressure, and sweating, among other things.

Many long-haulers never had laboratory confirmation of COVID-19, which can make it tricky to diagnose post-COVID-19 syndrome. Early on in the pandemic, tests were scarce. Many people who suspected they had COVID-19 self-isolated without getting a test, or were refused a COVID test when they requested one. And the tests themselves have not been entirely reliable; both diagnostic tests and antibody tests may return false negative results if taken too early or too late in the course of illness.

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. A mutation of the original SARS-CoV-2 virus — the D614G variant — has quickly become the most prevalent form of the virus seen around the world.

This mutation occurred on the coronavirus's spike proteins, protrusions on the surface of the virus that open the host cell and allow the virus to enter. About 1,300 amino acids serve as building blocks for a spike protein. In the D614G variant, the genetic instructions for just one of the spike protein's amino acids — number 614 — switched in the new variant from a "D" (short for aspartic acid) to a "G" (short for glycine).

Evidence is building that the D614G strain may spread more easily than the original strain. Infected individuals with this strain appear to have more virus in their upper respiratory tracts, and therefore may be more likely to spread infection to others. So far, the mutated strain has NOT seemed to cause more severe disease.

Mutations of coronaviruses, like all viruses, are to be expected. Scientists working on vaccines take this into account.

Whether people previously infected with the original strain can be infected again with this new and now more dominant strain is not yet known. But it's another reason why physical distancing, avoiding crowds when possible, wearing masks, and hand washing remain our best defense.

Which precautions are really necessary when it comes to preventing COVID-19?

Wear masks. Physically distance. Socialize outdoors. Avoid crowded indoor spaces. Wash your hands frequently. These are essential precautions you should take to reduce your risk of catching or spreading coronavirus.

But what about some other precautions you may be taking? Do they help, or is it okay to let them go? Let's take a look.

You don't need to wear gloves when running errands. It's true that a person can get infected if they touch a surface or object that has viral particles on it, then touch their mouth, nose, or eyes. But this is not the main way the virus spreads. What's more, gloves won't prevent this type of transmission, and may even make it more likely that you will touch your face. Instead, wash your hands before you leave the house, use hand sanitizer when you're out and about, and wash your hands again when you get back home. In between, try to avoid touching your face.

You don't need to disinfect groceries or takeout containers. The risk of infection from food or food packaging is very small. The CDC advises against using disinfectant intended for hard surfaces on cardboard or other grocery items, which can absorb the chemicals. If you are concerned about takeout, transfer food to your own serving dishes. And wash your hands and disinfect your counters after putting away your groceries or handling takeout containers.

Your mail can come out of quarantine. Mail does not pose a large risk, and putting your mail aside for several days before opening it is unnecessary. Once again, your best bet is to wash your hands after handling anything you bring in from outside.

You can invite your cleaners back into your home. If you've asked your cleaners to come back, request that they wear masks the entire time they are in your home. Leave the house while the cleaners are present if you can; otherwise, move to a different part of the house and close the door. Open windows to increase airflow throughout the house.

It's okay to go for a swim. Pools are relatively safe, because the coronavirus doesn't spread through water and chlorine is a disinfectant. Try to maintain physical distancing in crowded pools, but don't wear cloth masks in the water: they are difficult to breathe through when wet. Do wear a mask when changing, however, and minimize time in changing rooms, which are often crowded and not well ventilated.

The FDA recently granted emergency use authorization to a new rapid antigen test for COVID-19. How is it different from other tests on the market?

The FDA recently granted emergency use authorization (EUA) for a new diagnostic test for COVID-19. Results from this inexpensive test are available within 15 minutes.

The BinaxNOW COVID-19 Ag Card, as the test is known, detects antigen proteins on the surface of SARS-CoV-2, the virus that causes COVID-19. Unlike other diagnostic tests for COVID-19, BinaxNOW does not require a laboratory or other equipment to process or analyze the test results. This makes it portable and fast.

This test is approved for use in people who are suspected of having COVID-19, and must be done within seven days of when their symptoms began. A prescription is needed to get this test, which can be performed in authorized locations including doctor's offices and emergency rooms.

To perform the test, a sample obtained using a nasal swab is inserted into the BinaxNOW test card. The test is a lateral flow immunoassay, which works like a pregnancy test. The appearance of colored lines on the test strip indicates whether or not you have tested positive for COVID-19. The test comes with a smartphone app that can be used to share test results.

Positive test results are highly specific, meaning that if you test positive you are very likely to be infected, particularly if you are tested during the first week of infection when you are experiencing symptoms. False negatives are a bigger concern. As with other antigen tests, BinaxNOW can miss infections, producing negative test results in people who are actually infected.

Still, this test could have an important role during this pandemic. It offers a quick, easy, and inexpensive way to test more people, more quickly.

Is a person who has been infected with coronavirus protected from becoming infected again?

Most people who are infected with the COVID-19 virus produce antibodies, which are proteins that make it harder for the virus to infect cells. But antibodies are only one part of the body's immune response. T cells, for example, can destroy cells that are already infected. And memory B cells can quickly generate a strong antibody response to a virus the body has encountered before.

Antibody levels typically fall once the immediate threat of infection declines. Several new studies have found that COVID-19 antibody levels decline, but then stabilize and remain in the blood even two to three months after infection. Other recent studies found COVID-specific B cells and T cells in the blood, months after people recovered. This all suggests that the immune system would be ready to react quickly and strongly if re-exposed to the COVID-19 virus.

The laboratory evidence is promising. But the real evidence will come as more and more people who have recovered (rather than cells in a lab) are re-exposed to the virus.

Researchers in Hong Kong recently reported the first confirmed case of reinfection with the COVID-19 virus. The man was first infected in March, then declared to be recovered after two negative coronavirus tests. Four and a half months later, he tested positive for coronavirus on a saliva screening test administered at the Hong Kong airport upon his return from a trip to Europe. Scientists sequenced viral genetic material from the man's two infections and found significant enough differences to suggest two separate infections.

The man had experienced mild symptoms during his first infection and had no symptoms the second time he was infected. It's possible that while his immune system could not protect him against reinfection, it did help keep him from getting sicker during the second infection.

It's far too early to make any generalizations. We cannot know from one case of reinfection (among tens of millions of people who have been infected) how strong an average immune response will be, or how long that immune response will last.

It's also worth noting that someone who has been re-infected — even someone with no symptoms — has the potential to spread the virus to others. That means that everyone, even those who have recovered from coronavirus infection, should continue to wear masks and practice physical distancing.

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.

What is convalescent plasma? Does it help people with COVID-19?

When people recover from COVID-19, their blood contains antibodies that their bodies produced to fight the coronavirus and help them get well. Antibodies are found in plasma, a component of blood.

Convalescent plasma — literally plasma from recovered patients — has been used for more than 100 years to treat a variety of illnesses from measles to polio, chickenpox, and SARS. It is widely believed to be safe.

In the current situation, antibody-containing plasma from a recovered patient is given by transfusion to a patient who is suffering from COVID-19. The donor antibodies may help the patient fight the illness, possibly shortening the length or reducing the severity of the disease.

Though convalescent plasma has been used for many years, and with varying success, not much is known about how effective it is for treating COVID-19. A recent analysis of 35,000 hospitalized patients who received convalescent plasma to treat severe COVID-19 suggests that the therapy may reduce the risk of dying. The data comes from the ongoing Expanded Access Program (EAP) led by the Mayo Clinic. The researchers found that patients with (or at risk of) severe COVID-19 who received convalescent plasma within three days of diagnosis were less likely to die than patients who received convalescent plasma later in their illness.

The problem? The study has no control group. All patients who are eligible to get convalescent plasma under the EAP receive that treatment. As a result, questions remain as to whether, or the degree to which, convalescent plasma is effective for treating COVID-19; who would benefit from this treatment; and when in the course of illness convalescent plasma is most effective. (High demand to enroll in the program may have also unintentionally driven down enrollment in randomized, controlled studies of convalescent plasma across the country.)

Despite this, the FDA has issued an emergency use authorization (EUA) for convalescent plasma, which will make it easier for hospitals to provide the treatment to their patients.

What types of masks are most and least effective?

We know that wearing masks can help prevent the spread of coronavirus by blocking droplets that are emitted when someone coughs, sneezes, talks, or breathes. But which masks are best and worst?

Researchers at Duke University created a simple setup that allowed them to count the number of droplet particles released when people spoke the phrase "Stay healthy, people" five times in a row. First, the study participants spoke without a mask, and then they repeated the same words, each time wearing one of 14 different types of face masks and coverings.

As expected, medical grade N95 masks performed best, meaning that the fewest number of droplets got through. They were followed by surgical masks. Several masks made of polypropylene, a cotton/propylene blend, and 2-layer cotton masks sewn in different styles also performed well.

Gaiters ranked dead last. Also called neck fleeces, gaiters tend to be made of lightweight fabric and are often worn by athletes. Bandanas also ranked poorly.

A couple of simple tests can help you gauge the effectiveness of your mask: If you can see through your mask when you hold it up to the light, or can breathe through it easily, it's probably not doing much to prevent spread.

Do people without symptoms have the same amount of coronavirus in their bodies as people with symptoms? And 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 to 72 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 recent study compared the amount of coronavirus in the nose, throat, and lungs of symptomatic and asymptomatic adults infected with SARS-CoV-2 (the COVID-19 coronavirus). Both groups of patients had similar amounts of virus in their bodies throughout the infection. This study did not look at the degree to which people with asymptomatic infections may infect others.

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.

Who do masks protect: the wearer, others, or both?

We've known for some time that masks help prevent people from spreading the coronavirus to others. Based on an analysis of existing information, a new study contends that masks may also protect mask wearers from becoming infected themselves.

Different masks, writes the study author, block viral particles to varying degrees. If masks lead to lower "doses" of virus being inhaled, then fewer people may become infected, and those who do may have milder illness.

Researchers in China experimented with hamsters to test the effect of masks. They put healthy hamsters and hamsters infected with SARS-CoV-2 (the COVID-19 coronavirus) in a cage, and separated some of the healthy and infected hamsters with a barrier made of surgical masks. Many of the "masked" healthy hamsters did not get infected, and those who did got less sick than previously healthy "maskless" hamsters.

A similar experiment cannot ethically be done in humans. But researchers have studied doses of flu virus and found that people who inhaled a higher dose of flu virus were more likely to get sick and experience symptoms. Observations of coronavirus outbreaks in processing plants and on cruise ships also support the idea that masks may help protect mask wearers.

Without more research, we can't be certain that masks protect the wearer. But we do know they don't hurt, and that they protect others.

What is the difference between a PCR test and an antigen test for COVID-19?

PCR tests and antigen tests are both diagnostic tests, which means that they can be used to determine whether you currently have an active coronavirus infection. However, there are important differences between these two types of tests.

PCR tests detect the presence of the virus's genetic material using a technique called reverse transcriptase polymerase chain reaction, or RT-PCR. For this test, a sample may be collected through a nasal or throat swab, or a saliva sample may be used. The sample is typically sent to a laboratory where coronavirus RNA (if present) is extracted from the sample and converted into DNA. The DNA is then amplified, meaning that many of copies of the viral DNA are made, in order to produce a measurable result. The accuracy of any diagnostic test depends on many factors, including whether the sample was collected properly, when during the course of illness the testing was done, and whether the sample was maintained in appropriate conditions while it was shipped to the laboratory. Generally speaking, PCR tests are highly accurate. However, it can take days to over a week to get the results of a PCR test.

Antigen tests detect specific proteins on the surface of the coronavirus. They are sometimes referred to as rapid diagnostic tests because it can take less than an hour to get the test results. Positive antigen test results are highly specific, meaning that if you test positive you are very likely to be infected. However, there is a higher chance of false negatives with antigen tests, which means that a negative result cannot definitively rule out an active infection. If you have a negative result on an antigen test, your doctor may order a PCR test to confirm the result.

It may be helpful to think of a COVID antigen test as you would think of a rapid strep test or a rapid flu test. A positive result for any of these tests is likely to be accurate, and allows diagnosis and treatment to begin quickly, while a negative result often results in further testing to confirm or overturn the initial result.

How long after I start to feel better will be it be safe for me to go back out in public again?

The most recent CDC guidance states that someone who has had COVID-19 can discontinue isolation once they have met the following criteria:

  1. It has been more than 10 days since your symptoms began.
  2. You have been fever-free for more than 24 hours without the use of fever-reducing medications.
  3. Other symptoms have improved.

The CDC is no longer recommending a negative COVID-19 test before going back out in public.

Anyone who tested positive for COVID-19 but never experienced symptoms may discontinue isolation 10 days after they first tested positive for COVID-19.

Even after discontinuing isolation, you should still take all precautions when you go out in public, including wearing a mask, minimizing touching surfaces, and keeping at least six feet of distance away from other people.


More about COVID-19


Podcast: Back to school: It's never been more complicated (recorded 7/30/2020)

Sending kids back to school in the fall is always a hopeful time in America. For most families, school is a vital part of the community. With the surge in coronavirus in many areas of the country, getting kids back in the classroom safely will require a major re-evaluation to reduce transmission rates that can impact people of all ages. We talked to Allan Geller, a senior lecturer in the Department of Social and Behavioral Sciences at Harvard's T.H. Chan School of Public Health. Like it or not, for school teachers and administrators, things are going to be different. Don't expect the traditional.

Podcast: 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.

Podcast: COVID-19 and underlying conditions: Why symptoms may be more severe for people with chronic disease (recorded 5/6/20)

People who have diabetes, a heart condition, cancer, kidney disease or other underlying condition are impacted more severely if they contract the coronavirus. Harvard Medical School endocrinologist Dr. Enrique Caballero explains why. Dr. Caballero is on the staff of Brigham and Women's Hospital in Boston, Massachusetts, and is the director of diabetes education in the post-graduate medical education department at Harvard Medical School.

Podcast: Entendiendo como afecta la infección por COVID-19 a personas con enfermedades crónicas subyacentes (recorded 5/6/20)

Las personas que tienen diabetes, una afección del corazón o de los riñones u otra enfermedad crónica subyacente se ven afectadas más severamente si contraen el coronavirus. El Dr. Enrique Caballero, endocrinólogo de la Escuela de Medicina de Harvard explica la forma en que estas enfermedades favorecen infecciones severas por COVID-19 y como el coronavirus puede empeorar estas condiciones crónicas. El Dr. Caballero forma parte del personal del Hospital Brigham and Women's y es el director de educación en diabetes en el departamento de educación médica de posgrado de la Facultad de Medicina de Harvard en Boston, Massachusetts.


Reliable resources


Terms to know:

aerosols: infectious viral particles that can float or drift around in the air. Aerosols are emitted by a person infected with coronavirus — even one with no symptoms — when they talk, breathe, cough, or sneeze. Another person can breathe in these aerosols and become infected with the virus. Aerosolized coronavirus can remain in the air for up to three hours. A mask can help prevent that spread.

community spread (community transmission): is said to have occurred when people have been infected without any knowledge of contact with someone who has the same infection

contact tracing: a process that begins with identifying everyone a person diagnosed with a given illness (in this case COVID-19) has been in contact with since they became contagious. The contacts are notified that they are at risk, and may include those who share the person's home, as well as people who were in the same place around the same time as the person with COVID-19 — a school, office, restaurant, or doctor's office, for example. Contacts may be quarantined or asked to isolate themselves if they start to experience symptoms, and are more likely to be tested for coronavirus if they begin to experience symptoms.

containment: refers to limiting the spread of an illness. Because no vaccines exist to prevent COVID-19 and no specific therapies exist to treat it, containment is done using public health interventions. These may include identifying and isolating those who are ill, and tracking down anyone they have had contact with and possibly placing them under quarantine.

epidemic: a disease outbreak in a community or region

flattening the curve: refers to the epidemic curve, a statistical chart used to visualize the number of new cases over a given period of time during a disease outbreak. Flattening the curve is shorthand for implementing mitigation strategies to slow things down, so that fewer new cases develop over a longer period of time. This increases the chances that hospitals and other healthcare facilities will be equipped to handle any influx of patients.

incubation period: the period of time between exposure to an infection and when symptoms begin

isolation: the separation of people with a contagious disease from people who are not sick

mitigation: refers to steps taken to limit the impact of an illness. Because no vaccines exist to prevent COVID-19 and no specific therapies exist to treat it, mitigation strategies may include frequent and thorough handwashing, not touching your face, staying away from people who are sick, social distancing, avoiding large gatherings, and regularly cleaning frequently touched surfaces and objects at home, in schools, at work, and in other settings.

pandemic: a disease outbreak affecting large populations or a whole region, country, or continent

physical distancing: also called social distancing, refers to actions taken to stop or slow down the spread of a contagious disease. For an individual, it refers to maintaining enough physical distance (a minimum of six feet) between yourself and another person to reduce the risk of breathing in droplets or aerosols that are produced when an infected person breathes, talks, coughs, or sneezes.

presumptive positive test result: a positive test for the virus that causes COVID-19, performed by a local or state health laboratory, is considered "presumptive" until the result is confirmed by the CDC. While awaiting confirmation, people with a presumptive positive test result will be considered to be infected.

quarantine: separates and restricts the movement of people who have a contagious disease, have symptoms that are consistent with the disease, or were exposed to a contagious disease, to see if they become sick

SARS-CoV-2: short for severe acute respiratory syndrome coronavirus 2, SARS-CoV-2 is the official name for the virus responsible for COVID-19.

social distancing: also called physical distancing, refers to actions taken to stop or slow down the spread of a contagious disease. For an individual, it refers to maintaining enough physical distance (a minimum of six feet) between yourself and another person to reduce the risk of breathing in droplets or aerosols that are produced when an infected person breathes, talks, coughs, or sneezes. It is possible to safely maintain social connections while social distancing, through phone calls, video chats, and social media platforms.

virus: a virus is the smallest of infectious microbes, smaller than bacteria or fungi. A virus consists of a small piece of genetic material (DNA or RNA) surrounded by a protein shell. Viruses cannot survive without a living cell in which to reproduce. Once a virus enters a living cell (the host cell) and takes over a cell's inner workings, the cell cannot carry out its normal life-sustaining tasks. The host cell becomes a virus manufacturing plant, making viral parts that then reassemble into whole viruses and go on to infect other cells. Eventually, the host cell dies.

Image: Naeblys/Getty Images


Questions?

Harvard Health Publishing Coronavirus Resource Center Experts

The Harvard Health Publishing team would like to acknowledge the Harvard Medical School experts who have contributed their time and expertise: Steven A. Adelman, MD; Ashwini Bapat, MD; Suzanne Bertisch, MD, MPH; Emeric Bojarski, MD; Stephanie Collier, MD, MPH; Todd Ellerin, MD; Huma Farid, MD; Robert Gabbay, MD, PhD, FACP; Alan Geller, MPH, RN; Ellen S. Glazer, LICSW; Peter Grinspoon, MD; Sabra L. Katz-Wise, PhD; Anthony Komaroff, MD; Douglas Krakower, MD; Debi LaPlante, PhD; Howard E. LeWine, MD; Dara K. Lee Lewis, MD; Sharon Levy, MD, MPH; Kristina Liu, MD, MHS; Julia Marcus, PhD, MPH; Luana Marques, PhD; Claire McCarthy, MD; Chris McDougle, MD; Babar Memon, MD, MSc; Uma Naidoo, MD; Janelle Nassim, MD; Vikram Patel, MBBS, PhD; Edward Phillips, MD; Shiv Pillai, PhD, MBBS; Lee H. Schwamm, MD; Howard J. Shaffer, PhD, CAS; John Sharp, MD; Robert H. Shmerling, MD; Jacqueline Sperling, PhD; Fatima Cody Stanford, MD, MPH, MPA, FAAP, FACP, FTOS; Monique Tello, MD, MPH; Robyn Thom, MD; Karen Turner, OTR/L; Scott Weiner, MD; Anna R. Wolfson, MD.

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