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Coronavirus Resource Center

November 23, 2021

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

I lost my COVID-19 vaccination record card. What should I do?

When you got your first vaccine dose, you should have received a white, CDC-labeled COVID-19 Vaccination Record Card. The card is filled out by the vaccine provider and indicates which vaccine you got, and when and where you received your shot. When you receive your next vaccine dose or booster, the card is updated with information about the additional shot(s).

 If you lose your card, there are several things you can do:

  • Contact your vaccination provider (for example, your doctor, a pharmacy, a community health center, or a mass vaccination site).
  • Contact your primary care provider (PCP).
  • Contact your state health department’s immunization information system (IIS) by phone or online. Vaccination providers are required to report COVID-19 vaccinations to their IIS and related systems, and many states have systems set up to help you obtain a copy of your COVID vaccination record.
  • If you enrolled in v-safe or VaxText, you can access your vaccination information using those tools.
  • Your state health department may also be able to help.

Once you obtain your vaccine card, take a picture of it, and keep the photo on your phone as a backup copy.

When will children be able to get the COVID-19 vaccine?

In November 2021, the CDC recommended that children 5 to 11 years old be vaccinated with the Pfizer/BioNTech pediatric COVID-19 vaccine. The recommendation followed the FDA’s authorization of the vaccine for children in this age group.

As with older children and adults, 5-to-11-year-olds will need two doses of the Pfizer/BioNTech vaccine, spaced three weeks apart. But they will receive a lower dose (10 micrograms) compared to 30 micrograms for people 12 year and older.

In study data submitted by Pfizer to the FDA, 2,268 children, ages 5 to 11, received two 10-microgram doses of the COVID-19 vaccine, spaced three weeks apart, while a smaller group of children received a placebo. Antibody responses and side effects in the 5-to-11-year-olds were comparable to those of 16-to 25-year-old participants from a previous study.

A subsequent analysis compared COVID-19 infections in the vaccine and placebo groups. It found the Pfizer vaccine to be 90.7% effective at protecting against COVID-19 infection, compared to placebo. This was based on three cases of COVID-19 in vaccinated study participants, compared to 16 cases in the placebo group. There were no cases of severe COVID-19 or multisystem inflammatory syndrome in children (MIS-C) in either group during the study.

When making their decisions, both the FDA and CDC considered the benefits of the vaccine, the risks of COVID-19, and the risks associated with mRNA vaccines, particularly rare side effects such as the heart inflammation that has been seen after mRNA vaccination, especially in male adolescents and young adults. Ultimaely, they decided that the benefits of the vaccine outweigh the possible risks, but will continue to monitor safety data.

In May 2021, the FDA had expanded its EUA for the Pfizer/BioNTech COVID-19 vaccine to include adolescents 12 to 15 years old in May 2021. Previously, the Pfizer vaccine was authorized for use in children 16 years and older. A CDC report published in MMWR in October 2021 showed that 12- to 18-year-olds who’d gotten two doses of the Pfizer vaccine were 93% less likely than those who were unvaccinated to be hospitalized for COVID-19. COVID-related hospitalizations in children and adolescents are still relatively rare; the majority of participants in this study had at least one underlying medical condition that put them at increased risk for severe illness.

The Moderna and Johnson & Johnson vaccines are currently authorized for people 18 years and older. In June 2021, Moderna applied to the FDA for emergency use authorization (EUA) of their mRNA vaccine for use in children ages 12 to under 18 years. The FDA is continuing to evaluate safety data about the risk of myocarditis after vaccination, and recently notified the company that it may not complete its review until early 2022. Moderna announced promising results of a Phase 2/3 study in adolescents in May. The study enrolled 3,732 children ages 12 to 17. Two-thirds received two doses of the Moderna mRNA vaccine and one-third received a placebo. The immune response generated by the vaccine in adolescents was found to be at least as good as the immune response the vaccine generated in adults. Starting two weeks after the second vaccine dose, no cases of COVID-19 occurred in the vaccine group, compared to four cases in the placebo group. Vaccine side effects were mild to moderate, with injection site pain, headache, fatigue, muscle pain, and chills being the most common. The study did not identify any significant safety concerns. The results were announced in a press release.

In October 2021, Moderna released an interim analysis of their phase 2/3 study in children. For this part of the randomized, observer-blind, placebo-controlled trial, researchers enrolled 4,753 children ages 6 years to under 12 years of age. The children received either two doses of the Moderna vaccine, spaced 28 days apart, or two doses of placebo. The vaccine dose was 50 micrograms, which is lower than the 100-microgram dose authorized for adults, but the same as the dose recently authorized for the Moderna booster. One month after receiving their second dose, the vaccinated children in this study had antibody levels that were about 1.5 times higher than those seen in young adults after two 100-microgram vaccine doses. Most side effects were mild to moderate, and included fatigue, headache, fever, and pain at the injection site. The study was too small to measure rare side effects. The analysis was announced in a press release and has not been published or peer reviewed. Moderna will submit these results to the FDA, and is also studying their vaccine in children between the ages of 6 months and 6 years.

Age de-escalation studies, in which the vaccines are tested in groups of children of descending age, are done to confirm that the vaccines are safe and effective for each age group. They also identify the optimal dose, which must be effective, but with tolerable side effects.

The FDA reviews data from the de-escalation trials to decide whether to authorize the vaccines for each age group. The CDC then considers whether to issue a recommendation.

Which COVID-19 vaccine booster should I get?

As of November 2021, all adults ages 18 years and older are eligible to receive a single-dose COVID-19 vaccine booster shot. Those who initially received an mRNA vaccine (Pfizer/BioNTech or Moderna) can get their booster six months after their second shot, while those who received an initial dose of the Johnson & Johnson vaccine can get a booster dose two months after their initial vaccine.

The FDA and CDC are allowing individuals to select any COVID-19 vaccine (Pfizer/BioNTech, Moderna, or Johnson & Johnson) for their booster, either the same as (homologous) or different than (heterologous) their initial vaccine(s).

The FDA’s authorization was based, in part, on an NIH study that has not yet been peer reviewed or published. The study enrolled 458 adults who had received one of the three available COVID-19 vaccines at least three months earlier. The study participants each got a booster dose: one-third received a Pfizer/BioNTech booster, one-third received a Moderna booster, and one-third received a Johnson & Johnson booster. The researchers looked at immune response, side effects, and safety of the nine resulting vaccine combinations.

The researchers found that any vaccine-plus-booster combination substantially increased the level of neutralizing antibodies (antibodies that block the COVID virus from infecting cells). However, the increase was greatest in those who followed a Johnson & Johnson vaccine with an mRNA vaccine, in particular the Moderna vaccine. The increase in neutralizing antibodies was fourfold for Johnson & Johnson followed by a Johnson & Johnson booster; 35-fold for Johnson & Johnson followed by a Pfizer/BioNTech booster, and 76-fold for Johnson & Johnson followed by a Moderna booster. However, the Moderna booster dose used in this study contains twice as much antigen as the dose that the FDA has authorized for the Moderna booster. And, importantly, the study was not designed to directly compare vaccine regimens.

The study uncovered no new safety concerns, and side effects were similar to those people have experienced with COVID vaccinations across all primary and booster vaccines.

Given this and other evidence, it makes sense for most people who started with the Johnson & Johnson vaccine to consider boosting with an mRNA vaccine (Moderna or Pfizer/BioNTech). On the other hand, if you started with the Moderna vaccine, you might think twice before mixing and matching.

The FDA’s mix-and-match authorization makes booster shots less dependent on which vaccines are available and gives people more choices. For example, if you had an unpleasant reaction to your initial vaccine, you could choose a different one for your booster. Or, if you don’t remember which vaccine you started with, you can still get a booster.

The FDA and CDC did not recommend that particular groups of people seek out or avoid specific vaccines. However, it may be reasonable for young women to ask their doctor whether they should avoid a booster dose of the Johnson & Johnson vaccine, which is associated with increased risk of a rare but serious type of blood clot that has been more common in women ages 18 to 49 years. In addition, there has a been a higher-than-expected number of heart inflammation cases after vaccination with the mRNA COVID-19 vaccines in male adolescents and young men. Those who fall into that category may want to ask their doctor if they should avoid a Pfizer/BioNTech or Moderna booster.

Who can get a COVID-19 vaccine booster shot?

In November 2021, the FDA authorized, and the CDC endorsed, a single-dose COVID-19 vaccine booster for all adults ages 18 years and older. Those who initially received an mRNA vaccine (Pfizer/BioNTech or Moderna) can get their booster six months after their second shot, while those who received an initial dose of the Johnson & Johnson vaccine can get a booster dose two months after their initial vaccine.

Individuals may select any vaccine for their booster, either the same (homologous) or different (heterologous) than their initial vaccine(s).

Can I get my flu shot at the same time as my COVID-19 booster shot?

According to the CDC, you can get the COVID-19 vaccine and another vaccine, including the flu shot, at the same time. The CDC’s guidance applies to the initial or booster dose of the COVID-19 vaccine.

Getting both vaccines at the same visit does not compromise the effectiveness of either immunization. Side effects are generally the same for vaccines given together or separately. Of course, if you get the shots in different arms, you could experience soreness in both arms.

Many clinics are now offering both vaccines at the same visit. It’s best to get your flu shot by the end of October.

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

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.

More new questions and answers

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 indicate that children are capable of spreading the infection.

Though the 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. And a November 2021 study conducted by Harvard researchers determined that children carry live virus capable of infecting others.

The amount of virus found in children — their viral load — was not correlated with the severity of their symptoms. In other words, a child with mild or no symptoms may have just as many viral particles in their nose and mouth as a child that has more severe symptoms. So, the presence of a high viral load in infected children increases the likelihood that children, even those without symptoms, could readily spread the infection to others.

The bottom line? Public health measures are as important for kids and teens as they are for adults.

Is there an antiviral pill that can reduce my risk of being hospitalized if I get COVID-19?

At least two oral antiviral drugs have performed well in clinical trials and show promise in reducing the risk of COVID-related hospitalization and death.


In October 2021, Merck released promising study results about an oral antiviral drug to treat COVID-19. Compared to placebo, the antiviral drug, called molnupiravir, significantly reduced the risk of hospitalization and death in people with mild or moderate COVID-19 who were at high risk for severe COVID. Molnupiravir is under review by the FDA, which is scheduled to meet in late November to discuss whether the drug should be granted emergency use authorization (EUA).

The study results were based on data from 775 study participants from the US and around the world. To be eligible for the study, the participants had to have been diagnosed with mild-to-moderate COVID-19, have started experiencing symptoms no more than five days prior to their enrollment in the study, and have at least one risk factor that put them at increased risk for a poor outcome from COVID-19. None of the participants were hospitalized at the time they entered the study. About half of the study participants took the antiviral drug molnupiravir; four capsules, twice a day, for five days, by mouth. The remaining study participants took a placebo.

Patients taking molnupiravir were half as likely to be hospitalized or die from COVID-19 as those taking a placebo. Over the 29-day study period, 28 out of 385, or 7.3%, of participants who took molnupiravir were hospitalized, and no one in this group died. In the placebo group, 53 out of 377, or 14.1%, of participants were hospitalized, including eight participants in this group who died. The antiviral drug was effective against several COVID variants, including the Delta variant.

The study was randomized, placebo-controlled, and double-blind — the gold standard in study design. The results were announced in a press release and have not been peer-reviewed or published in a medical journal. According to the press release, the risk of adverse events and drug side effects was comparable in the molnupiravir and placebo groups.

Molnupiravir was developed by Merck and Ridgeback Biotherapeutics. It works by interfering with the COVID virus’s ability to replicate.


Interim study results released by Pfizer in a press release in November 2021 showed that its oral antiviral treatment, called Paxlovid, significantly reduced the risk of COVID-related hospitalization and death compared to a placebo. The company plans to ask the FDA to authorize the treatment.

The phase 2/3 study was randomized, double-blind, and placebo controlled. Study participants had symptomatic, confirmed early COVID-19, were at increased risk for severe illness due to age or an underlying medical condition, and were not hospitalized. They took either a placebo or the Paxlovid treatment twice a day for five days.

By 28 days after treatment, those who had taken Paxlovid within three days of symptom onset had an 89% reduced risk of COVID-related hospitalization or death compared to those who took a placebo. Study participants who started Paxlovid within five days of the start of symptoms had an 85% reduced risk compared to placebo. Side effects of Paxlovid and placebo were comparable, and generally mild. In consultation with the FDA, an independent committee recommended that the study be stopped early because of the apparent benefit of the treatment.

Paxlovid is a protease inhibitor antiviral therapy made up of a medicine called PF-07321332 and the HIV drug ritonavir. PF-07321332 was developed by Pfizer; it interferes with the ability of the coronavirus to replicate. Ritonavir slows the breakdown of PF-0732332 so that it remains active longer at higher amounts.

The prospect of having an oral antiviral to combat COVID-19 is exciting, but is not a substitute for getting vaccinated. The COVID vaccine remains more important than ever. We need layers of defense against this viral threat. Hopefully oral antiviral medications will be part of that defense.

Is the antidepressant drug fluvoxamine effective for treating COVID-19?

A large study published in Lancet Global Health in October 2021 found that the antidepressant fluvoxamine (Luvox), which may be taken by mouth at home, significantly reduces the risk of hospitalization in some COVID-19 patients at serious risk for severe illness.

The Lancet study enrolled nearly 1,500 adults in Brazil. Most study participants were unvaccinated, had symptomatic, early, confirmed COVID-19, and were at increased risk of serious illness due to underlying health problems. About half took a placebo while the other half were told to take one 100-mg fluvoxamine pill, twice a day, for 10 days.

The fluvoxamine group was significantly less likely than the placebo group (11% versus 16%) to need hospitalization or an extended emergency room stay. The randomized, placebo-controlled trial was conducted by an international team of researchers, and it confirmed preliminary findings published last year in JAMA.

Common side effects of fluvoxamine include headaches, nausea, diarrhea, dizziness, and sexual side effects. In the Lancet trial, tens of participants assigned to fluvoxamine stopped taking the drug because of side effects. In addition, because the study participants took the drug (or placebo) at home, they did not all take the medication as prescribed. But in this case, medication adherence made a difference: those who took fluvoxamine as directed on more than 80% of possible days were significantly less likely to die than those in the placebo group. But there was no significant difference between the number of people who died in the placebo group compared to the full fluvoxamine group, which included a wide range of adherence.

Fluvoxamine is in a class of antidepressants called selective serotonin reuptake inhibitors (SSRIs). It was approved by the FDA in 1994 and is used to treat obsessive-compulsive disorder (OCD) and anxiety. Fluvoxamine appears to work against COVID by reducing inflammation, which is a hallmark of severe COVID infection. The drug may also have antiviral properties. Because it is already on the market, doctors can prescribe it off-label for COVID patients they deem appropriate.

Additional, high-quality research will hopefully reproduce the Lancet study findings and answer remaining questions. For example, will fluvoxamine help symptomatic COVID patients who are vaccinated, or those who do not have risk factors for severe illness? And, will people who already take daily fluvoxamine to treat mental health issues also gain some protection against COVID-19?

What do I need to know about the AY.4.2 (Delta Plus) variant?

As viruses replicate, they may mutate, or slightly alter their genetic sequence. If a mutation is advantageous — making the virus more transmissible or able to sidestep immune protection — it’s more likely to survive and thrive. That’s what happened with the Delta variant, which was many times more contagious than the original SARS-CoV-2 virus and quickly became the dominant variant around the globe. A new variant called AY.4.2 (or Delta Plus), a descendent of the Delta variant, is now gaining attention.

The AY.4.2 variant makes up about 11% of sequenced cases in the United Kingdom. It has also been identified in a handful of US states, but at present is responsible for less than 0.1% of COVID-19 cases in the US. The WHO has not classified AY.4.2 as a variant of concern or a variant of interest.

Preliminary evidence from the United Kingdom suggests that AY.4.2 is not more likely to lead to hospitalization or cause severe disease. And in a White House briefing, the CDC director said there is no evidence that this variant is less susceptible to current vaccines and treatments. It also does not appear more adept at evading immune protection.

However, there is a lot we still don’t know about the AY.4.2 variant, including whether and to what extent it is more transmissible than the original Delta variant. At this point, it appears to be only slightly more contagious (10% to 15%). Its spread may also be influenced by human behaviors, such as whether people are masking indoors and the degree to which people in a community are vaccinated.

It seems very likely that we will be living with this virus, and its variants, for some time to come. The best way to minimize the emergence of new variants, and to protect ourselves from variants that already exist, is to vaccinate as many people around the world as possible. Why? Because the less the virus spreads, the less opportunity it has to replicate and mutate. For the same reason, it’s vital to mask indoors, optimize ventilation, get tested if you have symptoms or are exposed to someone with COVID-19, and isolate if you test positive.

What types of masks are most and least effective?

We know that wearing masks can help prevent the spread of coronavirus by blocking droplets, and smaller particles called aerosols, that are emitted when someone coughs, sneezes, talks, or breathes. But which masks are best and worst? For the general public, a properly fitted surgical mask is the best option, and should be worn whenever possible.

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 two-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.

Although the CDC recommends masks made of two or more layers of washable, breathable fabric, surgical masks are more effective than cloth masks at filtering out smaller particles. Regardless of the type of mask you wear, make sure it completely covers your nose and mouth and fits snugly against the sides of your face without leaving any gaps.

The CDC has information on how to improve the fit of your mask.

More about COVID-19

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.

booster: an additional dose of COVID-19 vaccine given after protection from the initial vaccine series begins to decline. A homologous booster is the same brand as the initial vaccine; a heterologous booster is a different brand than the initial vaccine.

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.

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.    

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.

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.

variants of concern: SARS-CoV-2 viruses with mutations that make them more likely to spread, evade vaccines, or make people sicker.

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, MDAshwini Bapat, MD; Nicole Baumer, MD, MEd; Suzanne Bertisch, MD, MPHJoseph R. Betancourt, MD, MPHBarry R. Bloom, PhDEmeric Bojarski, MDMelissa Brodrick, MEdAndrew E. Budson, MDStephanie Collier, MD, MPHTodd Ellerin, MDHuma Farid, MD; Elizabeth Pegg Frates, MD; Robert Gabbay, MD, PhD, FACPAlan Geller, MPH, RNEllen S. Glazer, LICSW; David C. Grabowski, PhD; Shelly Greenfield, MD, MPH; Ilona T. Goldfarb, MD, MPH; Peter Grinspoon, MDAbraar Karan, MD, MPH, DTM&HSabra L. Katz-Wise, PhDAlyson Kelley-Hedgepeth, MDAnthony Komaroff, MDDouglas Krakower, MDDebi LaPlante, PhDHoward E. LeWine, MDDara K. Lee Lewis, MDSharon Levy, MD, MPHKristina Liu, MD, MHSJulia Marcus, PhD, MPHLuana Marques, PhDClaire McCarthy, MDChris McDougle, MDBabar Memon, MD, MSc; Kristin Moffitt, MD; Uma Naidoo, MDJanelle Nassim, MDJustin NeimanVikram Patel, MBBS, PhDEdward Phillips, MDShiv Pillai, PhD, MBBSJohn Ross, MD, FIDSALee H. Schwamm, MDCatherine Ullman Shade, PhD, MEdHoward J. Shaffer, PhD, CASRoger Shapiro, MD, MPHJohn Sharp, MD; Amy C. Sherman, MD; Robert H. Shmerling, MDJacqueline Sperling, PhDFatima Cody Stanford, MD, MPH, MPA, FAAP, FACP, FTOS; Dawn Sugarman, PhD; Monique Tello, MD, MPHRobyn Thom, MDKaren Turner, OTR/LRochelle Wallensky, MD, MPHJanice Ware, PhD; Bobbi Wegner, PsyD; Scott Weiner, MDSarah Wilkie, MSAnna 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.

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