Coronavirus Resource Center

As coronavirus continues to spread, many questions and answers

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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 blog posts featuring experts discussing coronavirus and COVID-19 and our glossary for relevant terms.

New questions and answers

What do we know about the Johnson & Johnson adenovirus vaccine?

A vaccine developed by Johnson & Johnson, which requires only a single shot, appears to be 85% effective at preventing severe disease, including prevention of hospitalization and death due to COVID-19. The vaccine also appeared to be more than 80% effective at preventing severe COVID disease in South Africa, where the B.1.351 variant is more common. Early data suggest the vaccine may also result in milder illness with fewer symptoms in those who develop COVID-19 after vaccination. These findings were posted online by the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC), which analyzed clinical trial data ahead of its upcoming decision on whether or not recommend that the vaccine receive emergency use authorization (EUA).

VRBPAC analyzed data from Johnson & Johnson's ongoing phase 3 randomized, double-blind, placebo-controlled clinical trial, which is designed to evaluate the safety and effectiveness of the vaccine compared to placebo in adults ages 18 and older. The study enrolled nearly 45,000 participants; half received the COVID-19 vaccine and the other half received a placebo.

Protection was generally consistent across race and age groups. Worldwide, the study participants were 59% White/Caucasian, 45% Hispanic and/or Latinx, 19% Black/African American, 9% Native American, and 3% Asian. In addition, 34% of participants enrolled in the study were over age 60, and 41% had at least one medical condition that put them at increased risk for severe COVID illness. Results suggest the vaccine may be less effective in people 60 years and older with comorbid conditions like diabetes or heart disease; however, no COVID-related deaths or medical interventions occurred in this population of vaccinated study participants.

Common vaccine side effects included mild to moderate pain at the site of injection, headache, fatigue, and muscle aches. A few rare, unexpected side effects also occurred: 15 vaccinated study participants and 10 volunteers who got a placebo developed conditions related to blood clots; and six vaccinated volunteers (but none in the placebo group) developed a ringing in the ears called tinnitus.

The Johnson & Johnson vaccine uses a modified, harmless form of a human common-cold adenovirus to deliver into the body the genetic instructions for making the coronavirus spike protein. Human cells use the instructions to make copies of the spike protein. The body recognizes the spike protein as an invader and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.

In addition to the advantage of having a one-dose vaccine, the other point in favor of the J&J vaccine is ease of storage. It can be safely refrigerated for months and frozen for even longer, unlike the mRNA vaccines, which must be frozen (one at ultracold temperatures).

Will the COVID-19 mRNA vaccines work against the new coronavirus variants?

Mutations have led to at least three new, concerning coronavirus variants: the B.1.1.7 variant, which was first detected in the United Kingdom; the B.1.351 variant, which originated in South Africa; and the P.1 variant, which originated in Brazil. Early evidence suggests that the current mRNA vaccines are effective against the B.1.1.7 variant, but possibly less so against the others.

In laboratory studies, researchers tested the effectiveness of the Pfizer/BioNTech mRNA vaccine against mutations found in the B.1.1.7 and B.351 variants. They found that the neutralizing antibodies the patients had created in response to the vaccine blocked the virus containing mutations from the B.1.1.7 variant as effectively as it blocked the unmutated virus. However, the vaccine was less effective at protecting against virus containing mutations found in the B.1.351 variant.

The Moderna vaccine also performed well against the B.1.1.7 variant. However, it was also less effective against the B.1.351 variant; in a laboratory study, the vaccine resulted in fewer neutralizing antibodies being produced against the B.1.351 variant, compared to the unmutated virus and the B.1.1.7 variant.

Neither company has released data regarding the P.1. variant, which shares some of the same mutations as the B.1.351 variant.

More study is needed to see if the laboratory results hold up in real-world conditions.

It's important to remember that both the Pfizer/BioNTech and Moderna vaccines are extremely effective — 95% and 94.1%, respectively. Even with a drop in effectiveness, they will still provide protection. Moderna has announced that it is looking into potential benefits of adding a booster dose to their two-dose regimen.

Are there any groups of people who should not get the mRNA COVID-19 vaccine?

There are only a few groups of people who should not get the mRNA vaccine. They include people who

  • are allergic to any components of the mRNA vaccine, which include polyethylene glycol (PEG) and polysorbate
  • had an allergic reaction within the first 30 minutes after receiving the first dose of an mRNA COVID-19 vaccine.

If you have a history of allergic reactions to other (non-COVID) vaccines or to injectable medications, ask your doctor if it is safe for you to get one of the currently available mRNA vaccines.

People with weakened immune systems, including those with autoimmune conditions and those taking immune-suppressing treatment, are at increased risk for severe COVID illness. People in these groups can get an mRNA vaccine. However, there may be other safety considerations. If you fall into this category, talk to your doctor about your individual risks and benefits.

Finally, it is possible that convalescent plasma or monoclonal antibodies, both of which are used to treat COVID-19, could reduce the effectiveness of the vaccine. If you have received either of these treatments, wait 90 days before getting your vaccine.

I have a severe allergy. Can I get the mRNA COVID-19 vaccine?

There have been rare cases of people having a severe allergic reaction after receiving the mRNA COVID-19 vaccine. As a result, everyone getting an mRNA vaccine in the US must be observed for at least 15 minutes after getting their shot, so they can receive immediate medical treatment if they experience a severe allergic reaction.

Despite the small risk, most people with a history of severe allergy can safely get the mRNA COVID-19 vaccine. This includes people who are allergic to food, pollen, bee stings, and medications taken by mouth. If you have a history of severe allergy, tell the person administering your vaccine. You will be observed for at least 30 minutes, instead of the usual 15 minutes.

If you have a history of allergic reactions to injectable medications or other vaccines, the CDC recommends asking your doctor if you should get one of the currently available mRNA vaccines.

There are some people who should not get an mRNA COVID vaccine. You should not get one if you are allergic to any components of the mRNA vaccine, which include polyethylene glycol (PEG) and polysorbate. And you should not get the second dose of an mRNA vaccine if you had an allergic reaction within the first 30 minutes after receiving the first vaccine dose.

If you have questions regarding the safety of the COVID vaccine for you, your best option is to talk to your doctor.

What side effects can I expect from the COVID vaccine?

Minor side effects are common after COVID-19 vaccination. Almost everyone experiences arm pain at the injection site. Other symptoms can include low grade fever, body ache, chills, fatigue, and headache.

You can expect to feel better within 24 to 48 hours. Some people feel too unwell to go to work or perform their usually daily activities during this period. Contact your doctor if your symptoms have not improved by the third day.

Moving your sore arm around may help to relieve discomfort. If you have a fever, drink plenty of fluids. Over the counter pain relievers like ibuprofen or acetaminophen can also help with fever, pain, and other discomfort. However, it's best to not take a pain reliever right before getting your shot, because there is a chance this could blunt your immune response.

The good news: These side effects are a sign that the vaccine is working and that your body is building an antibody response. The currently available vaccines require two shots, and side effects are more likely to occur after the second shot.

Should I get the COVID-19 vaccine if I already had COVID-19?

Even people who have already gotten sick with COVID-19 may benefit from the vaccine, according to the CDC.

Here's what we know. COVID-19 can lead to serious illness and long-term complications, even in younger people and those without underlying medical conditions. We also know that it's possible for someone who has already had COVID-19 to be re-infected, though this is not common.

On the other hand, we don't know how long natural immunity to COVID-19 — the protection that results from having been sick — lasts. It's not clear if the strength or duration of natural immunity varies based on the severity of the initial illness. We also don't know how long immunity conferred by vaccines lasts.

During the initial deployment of the vaccine to front line workers and people in long-term care facilities like nursing homes, people eligible for the vaccine will get it regardless of whether or not they were previously infected. They are not being tested for antibodies prior to vaccination.

As scientists learn more about natural immunity after COVID illness, vaccination criteria based on the presence of antibodies may play a role in the future.

Once I get the COVID-19 vaccine, can I stop taking other precautions?

Early, emerging evidence suggests that the COVID-19 vaccine may reduce the chances that you will infect others. But more research is needed to know for certain if the vaccine reduces transmissibility. That's why, at least for now, you need to continue wearing a mask and physically distancing from others, even after you are vaccinated.

Will the COVID vaccine prevent me from infecting others?

Early evidence suggests that a person who has been vaccinated is less likely to infect others.

Two studies point in this direction. The first study looked at viral load — the amount of SARS-CoV-2 virus in a person's nose and throat, which can be spread to others. The study found that the higher a person's viral load, the more likely they were to spread the infection; the lower a person's viral load, the less likely they were to spread the infection. Results from the second study suggested that people who became infected with SARS-CoV-2 after getting a COVID vaccine had a lower viral load than people who were infected but had not had a COVID vaccine.

Taken together, the studies suggest that the COVID vaccine protects against both infection and transmission. However, more research is needed to confirm these findings.

For now, whether or not you have been vaccinated, you should continue wearing masks and maintaining physical distance in order to protect others who haven't yet gotten the vaccine.

Could an mRNA vaccine change my DNA?

An mRNA vaccine — the first COVID-19 vaccine to be granted emergency use authorization (EUA) by the FDA — cannot change your DNA.

mRNA, or messenger RNA, is genetic material that contains instructions for making proteins. mRNA vaccines for COVID-19 contain man-made mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the "spike" protein found on the surface of the COVID-19 virus. Soon after a cell makes the spike protein, the cell breaks down the mRNA into harmless pieces. At no point does the mRNA enter the cell's nucleus, which is where our genetic material (DNA) lives.

The immune system recognizes the spike protein as an invader and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.

Click here for more new questions and answers.

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

You've gotten the basics down: you're wearing your mask, avoiding crowds, and keeping your distance from friends and family. 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.

COVID-19 vaccines

Based on strong scientific evidence of safety and effectiveness, the FDA authorized the first COVID-19 vaccines less than one year after the first COVID-19 cases were reported. You may be excited, but cautious. You likely still have questions. How do the vaccines work? Who should get them? How long will protection last? Will the vaccine prevent me from infecting others?

Click here to learn more about COVID-19 vaccines.

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

Most people who become ill with COVID-19 can recover at home, and there are things you can do to feel better. The FDA has also authorized treatments that doctors may use to treat hospitalized COVID-19 patients, and to treat COVID-19 patients who are not hospitalized but are at risk for becoming severely ill. Researchers around the globe continue working hard to develop other effective treatments.

Click here to read more about measures that can help.

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.

More New Questions and Answers

Lately I've seen more people wearing two masks. Should I be double masking?

According to new guidance from the CDC, yes you should. The guidance is based on a lab study, published in MMWR, which used masked and unmasked dummies that released aerosol particles from a mouthpiece when they were simulated to cough or breathe. The study found that wearing a multilayered cloth mask over a surgical mask or wearing a tightly fitted surgical mask substantially increased the level of protection for both the mask wearer and others.

When double masking, the CDC recommends wearing a snug cloth mask over a surgical mask. Surgical masks provide better filtration, but tend to fit loosely. Cloth masks close any gaps and provide another layer of protection. Surgical masks are sometimes called medical masks or medical procedure masks.

Adjusting a surgical mask for a tighter fit using a method called "knotting and tucking" also offers good protection. To knot and tuck a surgical mask, knot the ear loops of a 3-ply face mask where they join the edge of the mask, then fold and tuck the unneeded material under the edges. For video instructions on how to knot and tuck a surgical mask, click here. Mask fitters, or mask braces, which are worn over a cloth or surgical mask, can also improve mask fit.

In the CDC's lab study, double masking or tight-fitting surgical masks reduced both transmission of and exposure to aerosols by about 95% compared to no masking.

How do saliva tests compare to nasal swab tests for diagnosing COVID-19?

Samples for COVID-19 tests may be collected through a long swab that is inserted into the nose and sometimes down to the throat, or from a saliva sample.

The saliva test is easier to perform — spitting into a cup versus submitting to a swab — and more comfortable. Because a person can independently spit into a cup, the saliva test does not require interaction with a healthcare worker. This cuts down on the need for masks, gowns, gloves, and other protective equipment.

Either saliva or swab samples may be used for PCR tests, which detect genetic material from the coronavirus. Swab or saliva samples can also be used for antigen tests, which detect specific proteins on the surface of the coronavirus.

A systematic review and meta-analysis published in JAMA Internal Medicine found that saliva- and nasal swab-based tests that used a technique similar to PCR were similarly accurate. A positive result on either test meant that it was accurate at diagnosing the infection 99% of the time. However, approximately 16 out of 100 people who are infected will be missed.

These results are very similar to prior studies, reinforcing that a single negative swab or saliva test does not mean you don't have COVID. If you have symptoms suggestive of COVID, presume you may still be infected to avoid transmitting the virus to others.

Do the newer COVID-19 variants spread more easily? And are they more dangerous?

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 at least three new, concerning coronavirus variants. One, called B.1.1.7, was first detected in the United Kingdom. Another, called B.1.351, originated in South Africa. A third, called P.1 originated in Brazil. All three variants have now been detected in countries around the globe.

All of these 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. All three variants share a key mutation (called N501Y) on the spike protein, which allows the virus to bind more tightly to human cells. This mutation makes the new variants more contagious than previous SARS-CoV-2 variants. The B.1.351 and P.1 variants also share a second mutation, called E484K, which might make it easier for them to re-infect someone who has already been infected or, possibly, someone who has been vaccinated.

The B.1.1.7 variant is estimated to be about 50% more transmissible than previous SARS-CoV-2 variants. Early data also suggest that it may be 30% to 50% more virulent, meaning that it is more likely to cause severe illness and death. Fortunately, existing COVID-19 vaccines appear to be effective against the B.1.1.7 variant.

The emergence of these highly transmissible variants is yet another reason why mask wearing, physical distancing, avoiding crowds, and getting vaccinated once you are eligible continue 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.

Is there an over-the-counter, at-home test for COVID-19?

The FDA has granted emergency use authorization (EUA) to the first COVID-19 test that can be obtained without a doctor's prescription and fully performed at home. The Ellume COVID-19 Home Test is approved for use in adults and in children age 2 and older, with or without COVID-19 symptoms.

To take the test, you collect a nasal swab, stir it in a vial of processing fluid, then place a drop of the fluid in an analyzer. The device, which detects coronavirus antigens, delivers a positive or negative test result to your smartphone within 20 minutes.

Like other antigen tests, this test is less accurate than "gold standard" PCR tests, but initial studies suggest the accuracy comes close to PCR testing. Until there is much more real-world experience with this home test, the FDA recommends interpreting any result with caution.

If you have COVID-like symptoms, you should self-isolate and contact your doctor whether your test is positive or negative. Your doctor will likely suggest a PCR test for confirmation. You should also self-isolate and call your doctor if you get a positive test result, even if you don't have symptoms. A negative test if you don't have symptoms makes it very unlikely that you are infected. However, you should continue to follow the standard prevention strategies of physical distancing, avoiding crowds, wearing a mask, and hand washing.

This test will be available in drugstores and is expected to cost about $30.

When can I discontinue my self-quarantine?

A full, 14-day quarantine remains the best way to ensure that you don't spread the virus to others after you've been exposed to someone with COVID-19. However, according to CDC guidelines, you may discontinue quarantine after a minimum of 10 days if you do not have any symptoms, or after a minimum of 7 days if you have a negative COVID test within 48 hours of when you plan to end quarantine.

What are monoclonal antibodies? Can they help treat COVID-19?

Three monoclonal antibody treatments for COVID-19 have been granted emergency use authorization (EUA) by the FDA. All three treatments may be used to treat non-hospitalized adults and children over age 12 with mild to moderate symptoms who have recently tested positive for COVID-19, and who are at risk for developing severe COVID-19 or being hospitalized for it. This includes people over 65, people with obesity, and those with certain chronic medical conditions.

Monoclonal antibodies are manmade versions of the antibodies that our bodies naturally make to fight invaders, such as the SARS-CoV-2 virus. All three of the FDA-authorized therapies attack the coronavirus's spike protein, making it more difficult for the virus to attach to and enter human cells.

The three monoclonal antibody treatments that have received EUA are bamlanivimab, made by Eli Lilly; a combination of casirivimab and imdevimab, made by Regeneron; and a combination of bamlanivimab and etesevimab, made by Eli Lilly. These treatments must be given intravenously in a clinic or hospital.

The three monoclonal antibody treatments were tested in separate clinical trials. Bamlanivimab alone and the combination of casirivimab and imdevimab were both found to significantly reduce the risk of being hospitalized or visiting the ER within 28 days after treatment, compared to placebo. The bamlanivimab/etesevimab combination was found to significantly reduce the risk of hospitalization or death within 29 days of treatment, compared to placebo.

These treatments are not authorized for hospitalized COVID-19 patients or those receiving oxygen therapy. They have not shown to benefit these patients and could lead to worse outcomes in these patients.

More about COVID-19

Podcast: 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.

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.

antibodies: proteins made by the immune system to fight infections. If the antibodies later encounter the same infection, they help prevent illness by recognizing the microbe and preventing it from entering cells.

antibody test: also known as a serologic test, an antibody test is a blood test that looks for antibodies created by your immune system. An antibody test can indicate if you were previously infected but is not a reliable way to determine whether you are currently infected.

antigen: a substance displayed on the surface of a microbe that stimulates the body to produce an immune response.

antigen test: a diagnostic test that detects specific proteins on the surface of the virus.

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.

diagnostic test: indicates whether you are currently infected with COVID-19. A sample is collected using a swab of your nose, your nose and throat, or your saliva. The sample is then checked for the virus's genetic material (PCR test) or for specific viral proteins (antigen test).

effectiveness: indicates the benefit of a vaccine in the real world.

efficacy: indicates the benefit of a vaccine compared to a placebo in the context of a clinical trial.

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.

false negative: a test result that mistakenly indicates you are not infected when you are.

false positive: a test result that mistakenly indicates you are infected when you are not.

herd immunity: herd immunity occurs when enough people become immune to a disease to make its spread unlikely. As a result, the entire community is protected, even those who are not themselves immune. Herd immunity is usually achieved through vaccination, but it can also occur through natural infection.

immunity: partial or complete protection from a specific infection because a person has either had that infection previously or has been vaccinated against it.

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

long-haulers: people who have not fully recovered from COVID-19 weeks or even months after first experiencing symptoms.

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.

monoclonal antibodies: laboratory-produced proteins designed to mimic naturally occurring antibodies that target specific antigens on viruses, bacteria, and cancer cells.

mRNA: short for messenger ribonucleic acid, mRNA is genetic material that contains instructions for making proteins.

mRNA vaccines: mRNA vaccines for COVID-19 contain synthetic mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the "spike" protein found on the surface of the COVID-19 virus. The body recognizes the spike protein as an invader, and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.

mutation: a change to a virus's genetic material that occurs when the virus is replicating. The change is passed on to future generations of the virus.

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.

polymerase chain reaction (PCR) test: a diagnostic test that detects the presence of the virus's genetic material.

post-viral syndrome: the constellation of symptoms experienced by COVID-19 long haulers. These symptoms may include fatigue, brain fog, shortness of breath, chills, body ache, headache, joint pain, chest pain, cough, and lingering loss of taste or smell.

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.

spike protein: a protein on the surface of the SARS-CoV-2 virus that binds to and allows the virus to enter human cells.

variant: a virus containing one or more mutations that make it different from a version of the virus that has been circulating.

vector: a harmless capsule. In a vaccine, a vector may be used to deliver a substance into the body in order to prompt an immune response.

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.

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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; Joseph R. Betancourt, MD, MPH; Barry R. Bloom, PhD; Emeric Bojarski, MD; Melissa Brodrick, MEd; Andrew E. Budson, MD; Stephanie Collier, MD, MPH; Todd Ellerin, MD; Huma Farid, MD; Robert Gabbay, MD, PhD, FACP; Alan Geller, MPH, RN; Ellen S. Glazer, LICSW; Ilona T. Goldfarb, MD, MPH; Peter Grinspoon, MD; Abraar Karan, MD, MPH, DTM&H; Sabra L. Katz-Wise, PhD; Alyson Kelley-Hedgepeth, MD; 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; Justin Neiman; Vikram Patel, MBBS, PhD; Edward Phillips, MD; Shiv Pillai, PhD, MBBS; John Ross, MD, FIDSA; Lee H. Schwamm, MD; Catherine Ullman Shade, PhD, MEd; Howard J. Shaffer, PhD, CAS; Roger Shapiro, MD, MPH; 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; Rochelle Wallensky, MD, MPH; Janice Ware, PhD; Scott Weiner, MD; Sarah Wilkie, MS; Anna R. Wolfson, MD.

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.