Recent Blog Articles
Can we prevent depression in older adults by treating insomnia?
Want to try veganism? Here's how to get started
Vitamin B6 flies under the radar: Are you getting enough?
The formula shortage is hurting families: What parents should know and do
Gyn Care 101: What to know about seeing a gynecologist
Swimming lessons save lives: What parents should know
Strong legs help power summer activities: Hiking, biking, swimming, and more
What is a successful mindset for weight loss maintenance?
French fries versus almonds: Calorie for calorie, which comes out on top?
Summer camp 2022: Having fun and staying safe
Coronavirus Resource Center
As coronavirus continues to spread, many questions and answers
Learn more about:
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
Who can get a COVID-19 vaccine booster shot?
As of March 2022, the following groups are eligible for a second booster shot:
- everyone ages 50 years and older who received their first booster (Pfizer/BioNTech, Moderna, or Johnson & Johnson) at least four months ago
- certain immunocompromised individuals ages 12 years and older who received their first booster at least four months ago.
The CDC is only recommending mRNA vaccines for second boosters, and has stated that a second booster is "…especially important for those 65 and older and those 50 and older with underlying medical conditions that increase their risk for severe disease from COVID-19…"
The CDC recommends a single-dose COVID-19 vaccine booster for all adults ages 18 years and older. Those who initially received the Pfizer/BioNTech or Moderna mRNA vaccine can get their booster five months after their second shot, and those who received an initial dose of the Johnson & Johnson vaccine can get a booster dose two months after their initial vaccine. Adults may select any vaccine for their booster, either the same (homologous) or different (heterologous) than their initial vaccine(s). However, the FDA has limited use of the Johnson & Johnson vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines.
The CDC also recommends a single-dose Pfizer/BioNTech COVID-19 booster shot for children ages 5 years and older, at least five months after getting their second dose of that vaccine. As of now, individuals in this age group are only authorized to receive the Pfizer/BioNTech vaccine.
What should I consider before getting a second COVID-19 vaccine booster?
In March 2022, the CDC recommended a second booster shot for anyone ages 50 years and older, as well as certain immunocompromised individuals ages 12 years and older, at least four months after their first booster. The CDC noted: "This is especially important for those 65 and older, and those 50 and older with underlying medical conditions that increase their risk for severe disease from COVID-19, as they are the most likely to benefit from receiving an additional booster dose at this time."
Data from the CDC has shown that the effectiveness of booster shots decreases over time. A study published in MMWR reported that vaccine effectiveness against COVID-related hospitalizations dropped from 91% within two months after a booster dose to 78% four months after a booster dose. Data for this study were collected during the Omicron surge.
A second booster shot may help protect against COVID-related death in older adults, according to a small preprint study from Israel. Of the study participants, all of whom were ages 60 years and older, 232 of the 234,868 people who received one booster shot had a COVID-related death, compared to 92 of the 328,597 people who received two booster shots. That means people who got a second booster were 78% less likely to die than those who got a single booster. This was a significant difference.
The benefits of a second booster for younger, healthier populations are less certain. In a small report published in NEJM, researchers reported only "marginal benefits" of a second booster for middle-aged healthcare workers compared with a single booster. Although the second booster was safe and resulted in a large bump in neutralizing antibodies, vaccine efficacy was low against COVID infections.
Although vaccine effectiveness decreases over time, especially against infection and symptomatic infection, vaccines are still the best way to protect against severe illness. Consider the following factors when thinking about a second booster shot for yourself or a loved one.
- Age. The risk of severe COVID-related illness increases with age. A second booster increases neutralizing antibody levels, and there is evidence that a second booster protects older people from COVID-related death. The CDC has noted that a second booster is especially important for those 65 years and older.
- Underlying medical conditions. Immunocompromised individuals and those with certain underlying medical conditions are at increased risk for severe illness, hospitalization, and death due to COVID. The CDC has said that these groups are among those most likely to benefit from a second booster.
- Timing. There is some evidence that longer intervals between booster doses result in a stronger and longer-lasting immune response. However, that can leave you more vulnerable between booster doses.
- Goals. Are you trying to reduce your risk of any infection, symptomatic infection, or severe illness and hospitalization? The answer may depend on your age, medical history, and other factors, and could influence how you think about a second booster.
- What’s next? Omicron-specific mRNA vaccines are in development and may be available later this year.
You can take a variety of precautions against infection in addition to vaccination. These include masking indoors, not eating in indoor restaurants, and avoiding crowded spaces. You can adopt or discard layers of protection depending on COVID risk levels in your community.
Which COVID-19 vaccine booster should I get?
Adults ages 18 years and older may select a COVID-19 vaccine booster that is the same as (homologous) or different than (heterologous) their initial vaccine(s). Only mRNA vaccines (Pfizer/BioNTech and Moderna) have been authorized for second boosters.
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.
Although Johnson & Johnson’s vaccine is still available as an option for the first booster, in May 2022 the FDA limited use of the Johnson & Johnson vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines, due to concerns about a rare, but potentially fatal, blood clotting disorder.
The CDC also recommends boosters for children ages 5 to 17 years. Right now, only the Pfizer/BioNTech vaccine is authorized for this age group.
Do COVID-19 vaccines work against the newer variants?
mRNA COVID-19 vaccines have not protected as well against infection with Omicron as they did against previous SARS-CoV-2 variants. However, the vaccines continue to significantly reduce the chance of severe symptoms, hospitalization, and death, especially for people who have received a booster dose.
Research published in MMWR looked at the medical records of nearly 88,000 people across the US hospitalized with COVID-like symptoms between late August 2021 and early January 2022, which included periods during which both the Delta and Omicron variants were predominant. The data showed that full vaccination plus a booster was 94% effective in protecting against hospitalization with the Delta variant and 90% effective in protecting against hospitalization with the Omicron variant. Protection against hospitalization dropped significantly in people who had gotten their second vaccine dose more than six months prior and who had not gotten a booster dose.
Protection against severe disease and hospitalization in people who are vaccinated compared to those who are unvaccinated is striking. Additional data published by the CDC showed that unvaccinated Americans ages 50 to 64 years were 44 times more likely to be hospitalized than those who were vaccinated and boosted. Unvaccinated Americans ages 65 and older were 49 times more likely to hospitalized than their vaccinated and boosted counterparts.
How might boosters help? Booster-generated antibodies are not more specific to the Omicron variant. But the sheer increase in antibody levels helps enhance our immunity.
But vaccines do more than generate antibodies. They also stimulate other parts of the immune response, including T cells, which attack infected cells and recruit other immune cells to protect against severe illness. The part of the virus targeted by T cells was largely unaffected by mutations in the Omicron variant, so the T cell response in people who are immunized should remain strong.
The evidence reinforces the same important messages. If you are not vaccinated, get vaccinated. If you are eligible for a booster, get boosted. And everyone should continue to mask indoors, avoid crowds, and follow other preventive measures.
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. You may also be able to get a digital copy of your vaccine record that you can store on your smartphone.
I am pregnant and plan to eventually breastfeed my baby. Is it safe for me to get a COVID-19 vaccine?
The CDC recommends that women who are pregnant, thinking about becoming pregnant, or were recently pregnant — including those who are breastfeeding — should get vaccinated against COVID-19. The American College of Obstetrics and Gynecology (ACOG) and the Society for Maternal-Fetal Medicine also agree that all pregnant and breastfeeding individuals should be vaccinated.
Here are some factors to consider. First, although the actual risk of severe COVID-19 illness and death among pregnant individuals is very low, it is higher when compared to nonpregnant individuals from the same age group. In addition, COVID-19 increases risk for premature birth, stillbirth, and possibly also for other undesirable pregnancy outcomes. Results from a large, observational study from Scotland conducted between December 2020 and October 2021 showed that risks to both mother and baby are substantially higher in pregnant women who are unvaccinated, compared to those who are vaccinated.
Evidence supporting the safety of COVID vaccines for pregnant women and their babies continues to grow. One study published in MMWR looked at data from more than 40,000 pregnant women between December 2020 and July 2021. About 10,000 of these women received a COVID-19 vaccine (typically an mRNA vaccine, either Pfizer/BioNTech or Moderna) during their pregnancy, most during their second or third trimester. Women who were vaccinated against COVID-19 while pregnant were no more likely than unvaccinated women to give birth prematurely or have a baby that was small for its gestational age.
A study published in NEJM in October 2021 analyzed safety data collected by the CDC. The researchers looked at data from nearly 2,500 women who received a COVID-19 vaccine, either before becoming pregnant or during their first 20 weeks of pregnancy, and found that they did not have an increased risk of miscarriage. A previous study, conducted by the CDC and published in NEJM, found the COVID-19 vaccines to be safe when given during the second or third trimester.
Increasing evidence shows that vaccine-generated antibodies pass from mother to baby and protect newborns for several months after birth. A small study published in the American Journal of Obstetrics and Gynecology found that mRNA vaccines effectively produce antibodies that protect against SARS-CoV-2 in women who are pregnant or breastfeeding, and that this immunity is passed from mother to newborn through the placenta and breast milk. A study published in JAMA found that 98% of babies born to mothers who received an mRNA COVID-19 vaccine during pregnancy had detectable levels of antibodies two months after birth, and 57% of babies had detectable antibody levels six months after birth. And a report published in MMWR found that babies born to mothers who received two doses of an mRNA COVID-19 vaccine during pregnancy were 61% less likely to be hospitalized with COVID in their first six months of life than babies born to mothers who were not vaccinated while pregnant. Protective antibodies are particularly important for infants because COVID vaccines are not authorized for babies younger than 6 months.
mRNA vaccines do not contain any virus, so they cannot cause COVID-19 in a woman or her baby. And our bodies quickly break down and eliminate mRNA particles used in the vaccine, so they cannot reach or cross the placenta.
Similar to any decision regarding over-the-counter medications and supplements during pregnancy, your own doctor is in the best position to advise you based on your personal health risks and preferences.
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.
What is "Test to Treat"? Could it help me get antiviral treatment for COVID-19?
Test to Treat is a government initiative that makes it faster and easier for people with COVID-19 to obtain treatment. This is important because antiviral treatments for COVID-19 must be started within five days of a positive test or the start of symptoms. With Test to Treat, a person can get tested, get a prescription, and get their prescription filled, all in one place.
Here’s how it works. If you think you may have COVID-19, go to a Test to Treat site to get tested. If you test positive you will meet with a healthcare provider and, if you are eligible, will receive a prescription for antiviral treatment. You can then get your prescription filled at the same site.
A few things to keep in mind:
- You can bring a positive at-home test to a Test to Treat site.
- A healthcare provider at the Test to Treat site may ask about your medical history or other medications you take in order to make sure you are eligible for treatment.
- The two antiviral treatments being prescribed and filled at Test to Treat sites are Paxlovid and molnupiravir (Lagevrio).
The Test to Treat web-based locator can help you find a Test to Treat site near you. You can also call 800-232-0233 to get help in English, Spanish, and more than 150 other languages.
What therapies can help people who are at increased risk of severe COVID-19 to avoid hospitalization?
There is currently one FDA-authorized monoclonal antibody treatment that 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. The therapy is bebtelovimab, made by Eli Lilly. It must be given intravenously (by IV) soon after developing symptoms.
In laboratory tests, bebtelovimab was effective against BA.2, which is now the most common SARS-CoV-2 variant in the U.S.
In addition, the FDA has authorized the oral antiviral medications Paxlovid and molnupiravir, which have been shown to lower the risk of hospitalization and death in people who are at increased risk of severe COVID-19 illness.
How does COVID-19 affect children?
Children, including very young children, can develop COVID-19. Many of them have no symptoms. Those that do get sick tend to experience milder symptoms such as low-grade fever, fatigue, and cough.
In a paper published in March 2022 in the journal Pediatrics, researchers described more frequent and severe croup in infants and young children (too young to be vaccinated) infected with COVID-19 during the Omicron surge. Croup can occur when a viral infection such as SARS-CoV-2 causes the voice box, larynx, and bronchial tubes to become inflamed and swollen. Children with croup have a "barking" cough and noisy or high-pitched breathing.
Some children have had other severe complications of COVID-19, but this has been less common. Children with underlying health conditions may be at increased risk for severe illness.
Another potentially severe and dangerous complication can occur in children. Called multisystem inflammatory syndrome in children (MIS-C), it can lead to life-threatening problems with the heart and other organs in the body. In this condition, different body parts, such as the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs, can become inflamed.
Symptoms of MIS-C can include
- fever lasting more than a couple of days
- "bloodshot eyes"(redness of the white part of the eye)
- vomiting and/or diarrhea
- a large, swollen lymph node in the neck
- neck pain
- red, cracked lips
- a tongue that is redder than usual and looks like a strawberry
- swollen hands and/or feet
- irritability and/or unusual sleepiness or weakness.
Many conditions can cause symptoms similar to those of MIS-C. Your doctor will first want to know if your child has been around someone who has tested positive for the virus and will ask about all of the above symptoms. Results of the physical examination, a COVID-19 diagnostic or blood antibody test, and other medical tests that check for inflammation and how organs are functioning can support the diagnosis of MIS-C.
Call the doctor if your child develops symptoms, particularly if their fever lasts for more than a couple of days. If the symptoms get any worse or just don't improve, call again or bring your child to an emergency room.
Doctors have had success using various treatments for inflammation, as well as treatments to support organ systems that are having trouble. While there have been some deaths, most children who have developed MIS-C have recovered.
The journal Lancet Child & Adolescent Health published a study that looked at the long-term health effects of MIS-C on 46 children hospitalized with MIS-C between April and September 2020. All of the children had systemic inflammation; most also had problems related to gastrointestinal, heart, and kidney function, and clot formation. By six months after the children were discharged from the hospital, most of these problems had resolved, without lasting organ damage in most cases. About one-third of the children continued to have muscle weakness, fatigue, and mental health difficulties. But the study could not determine whether these effects were due to MIS-C in particular, or to hospitalization, or other factors.
Who is at highest risk for getting very sick from COVID-19?
Age is the strongest risk factor for severe COVID-19 illness. The risk of serious illness increases steadily with age, especially for those with underlying medical problems. In addition, a person's risk of severe illness from COVID-19 increases as the number of underlying medical conditions they have increases.
According to the CDC, adults of any age with the following conditions can be more likely to get severely ill from COVID-19:
- Cancer, cancer treatment, and history of cancer
- Chronic kidney disease
- Chronic liver disease, including alcohol-related liver disease, nonalcoholic fatty liver disease, autoimmune hepatitis, and cirrhosis (scarring of the liver)
- Chronic lung diseases, including asthma (moderate to severe), bronchiectasis (thickening of the lungs' airways), bronchopulmonary dysplasia (chronic lung disease affecting newborns), COPD (including chronic bronchitis or emphysema), interstitial lung disease (damaged or scarred lung tissue), pulmonary embolism (blood clot in the lungs), and pulmonary hypertension (high blood pressure in the lungs)
- Cystic fibrosis
- Dementia or other neurological conditions
- Diabetes (type 1 or type 2)
- Disabilities, including attention-deficit/hyperactivity disorder (ADHD), cerebral palsy, birth defects, intellectual and developmental disabilities, learning disabilities, spinal cord injuries, and Down syndrome. People with any type of disability that makes it more difficult to do certain activities or interact with the world around them, including people who need help with self-care or daily activities, may be at increased risk for getting very sick from COVID-19.
- Heart conditions, such as heart failure, coronary artery diseases, or cardiomyopathies (diseases of the heart muscle that make it harder for the heart to pump blood to the rest of your body), and possibly high blood pressure (hypertension)
- HIV (human immunodeficiency virus) infection
- Immunocompromised state (weakened immune system), including from inherited conditions (including primary immunodeficiency) or prolonged used of corticosteroids or other immune-weakening medicines
- Mental health conditions, including depression and schizophrenia spectrum disorders
- Overweight and obesity (body mass index [BMI] of 25 or higher)
- Physical inactivity
- Pregnancy and recent pregnancy
- Sickle cell disease, thalassemia, or other hemoglobin blood disorders
- Smoking, current or former
- Solid organ or blood stem cell transplant, including bone marrow transplant
- Stroke or cerebrovascular disease, which affects blood flow to the brain
- Substance use disorders such as alcohol, opioid, or cocaine use disorder
Everything we know underscores the importance of maintaining health-promoting behaviors, even as restrictions begin to ease, especially if you have one or more underlying medical conditions. To reduce your risk of getting sick, get vaccinated and boosted as soon as you are eligible, wear a mask indoors, especially when community levels of COVID are elevated, maintain a physical distance of at least six feet when you're around other people, and wash your hands often.
Should I wear a face mask?
The coronavirus that causes COVID-19 is primarily transmitted through viral particles that float in the air or through droplets containing virus. Even people who are infected but do not have symptoms, or have not yet developed symptoms, can infect others. Masks reduce the amount of virus we breathe in and breathe out. Combined with the vaccines and boosters, masks provide a one-two punch that reduces the risk of spread. Masks also provide protection for the wearer, even those who are fully vaccinated.
As the latest COVID surge relaxes its grip in the US, many states, towns, and schools are removing their indoor mask mandates. The CDC also issued updated guidelines, tying mask use recommendations to levels of the virus in a given community. COVID levels may be categorized as low, medium, or high, and are calculated by looking at hospital beds being used by COVID patients, COVID-related hospital admissions, and the total number of new COVID-19 cases in an area. You can click here to check the COVID level in your county.
According to the new CDC guidelines, everyone should mask indoors in public when COVID levels are high. People who are immunocompromised or at high risk for severe illness are encouraged to mask indoors when COVID levels are medium. When community levels are low, individuals can decide whether to mask indoors based on their individual risks and preferences.
Here are some points to consider as you decide whether you and your family should continue masking indoors.
- We’re still in the midst of a pandemic. As of late February 2022, there are nearly 2,500 COVID deaths per day in the US.
- Your decision should reflect your personal health risks: if you or a member of your family is at increased risk for infection or severe COVID illness, or if you are unvaccinated, continue masking indoors.
- Masking policies can’t always keep up with the virus. When COVID cases are high, consider masking indoors regardless of whether there’s a mask mandate in place.
- Your decision to mask indoors may change over time, and you may return to wearing a mask indoors after a period of not masking indoors.
- Masking reduces the risk of spread to vulnerable populations: young children who are not yet eligible for vaccines, people with weakened immune systems, older adults who are at increased risk for severe illness, and others who are unvaccinated.
- Masks don’t just help to flatten the curve; they also help to prevent surges from happening in the first place.
A high-quality, well-fitting mask provides good protection even if people around you are unmasked. High quality KN95, KF94, and N95 masks have the tightest fit and the best filtration. Make sure your mask completely covers your nose and mouth, and fits snugly against the sides of your face without leaving any gaps.
Transmission is much less likely to occur outdoors, and masks are not needed in most outdoor settings.
- Brain fog: Memory and attention after COVID-19
- Masks save lives: Here's what you need to know
- Pandemic challenges may affect babies — possibly in long-lasting ways
- Thinking about holiday gatherings? Harvard Health experts weigh in
- Wondering about COVID-19 vaccines for children 5 to 11?
- Preparing for the holidays? Don't forget rapid tests for COVID-19
- Thinking about COVID booster shots? Here's what to know
- World Health Organization
- Johns Hopkins University COVID-19 Interactive Map
- Harvard Medical School's HMX Online Learning team is offering a selection of immunity-related videos and interactive materials to help with understanding how the body reacts to threats like the coronavirus that causes COVID-19, and the role that vaccines can play in generating an immune response.
- Resources on Health Disparities and COVID-19
Interested in participating in COVID-19 research by tracking daily symptoms through a simple app? Help doctors and scientists at Massachusetts General Hospital and Harvard T.H. Chan School of Public Health study the symptoms of COVID-19 and track the spread of this virus by downloading the COVID Symptom Study app.
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.
Image: Naeblys/Getty Images
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; Nicole Baumer, MD, MEd; 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; Elizabeth Pegg Frates, MD; Robert Gabbay, MD, PhD, FACP; Alan Geller, MPH, RN; Ellen S. Glazer, LICSW; David C. Grabowski, PhD; Shelly Greenfield, MD, MPH; 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; Kristin Moffitt, MD; 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; Amy C. Sherman, MD; Robert H. Shmerling, MD; Jacqueline Sperling, PhD; Fatima Cody Stanford, MD, MPH, MPA, FAAP, FACP, FTOS; Dawn Sugarman, PhD; Monique Tello, MD, MPH; Robyn Thom, MD; Karen Turner, OTR/L; Rochelle Wallensky, MD, MPH; Janice Ware, PhD; Bobbi Wegner, PsyD; 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.
You might also be interested in…
COVID-19, Flu, and Colds
Any given year, we’ll collectively come down with one billion colds and up to 45 million cases of flu, while the number of new cases of COVID-19 keeps rising. In this guide, you will learn how to avoid getting any of these three viral infections, and, if you do get sick, what you can do to feel better. You’ll also learn when your condition is serious enough to call a doctor. The report also provides specific information about high-risk groups for whom COVID and the flu can be very serious.
Free Healthbeat Signup
Get the latest in health news delivered to your inbox!