Recent Blog Articles
Period equity: What is it, why does it matter?
Pandemic challenges may affect babies — possibly in long-lasting ways
4 immune-boosting strategies that count right now
If you have knee pain, telehealth may help
How to address opposition in young children
New study investigates treatment-associated regrets in prostate cancer
Minimizing successes and magnifying failures? Change your distorted thinking
Are poinsettias, mistletoe, or holly plants dangerous?
Waiting for motivation to strike? Try rethinking that
Thinking of trying Dry January? Steps for success
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
Why is the CDC recommending one of the mRNA COVID-19 vaccines over Johnson & Johnson’s vaccine?
In December 2021, the CDC stated a preference for one of the mRNA COVID-19 vaccines (Pfizer/BioNTech or Moderna) over Johnson & Johnson’s adenovirus COVID-19 vaccine. The CDC made the decision because of growing evidence that Johnson & Johnson’s vaccine increases the risk of blood clots. Although very rare, this problem can be serious and even lead to death.
The blood clots in question involve blood vessels in the brain, lungs, abdomen, and legs, and are accompanied by low levels of blood platelets. This combination is referred to as thrombosis and thrombocytopenia syndrome, or TTS, an abbreviation of the medical terms for the two conditions.
Since the FDA granted emergency use authorization (EUA) for the Johnson & Johnson vaccine in late February 2021, nearly 17 million doses of the one-dose vaccine have been given. A total of 54 cases of TTS, including nine deaths, were reported in people who received the Johnson & Johnson vaccine through August 31, 2021. TTS has been seen in men and women across age ranges, but the highest risk was seen in women ages 30 to 49 years.
The Johnson & Johnson COVID-19 vaccine will still be available in the US to people who cannot or do not want to get an mRNA vaccine. The vaccine’s label and fact sheet list symptoms of TTS, and urge anyone who experiences them after receiving the Johnson & Johnson vaccine to seek immediate medical attention.
While the risk of experiencing a blood clot after vaccination is very low, anyone who experiences the following symptoms after receiving the Johnson & Johnson vaccine should seek immediate medical care:
- severe or persistent headache
- chest pain
- blurred vision
- severe pain in your abdomen
- leg swelling
- shortness of breath
- tiny red spots under the skin
- new or easy bruising.
Will COVID-19 vaccines work against the Omicron variant?
It’s still early, but data looking at how well COVID-19 vaccines will protect against the Omicron variant suggest that current vaccines do not protect as well against infection with Omicron as they did against previous SARS-CoV-2 variants. However, the evidence also suggests that vaccines significantly reduce the chance of severe symptoms, hospitalization, and death, especially for people that have received a booster.
A number of studies, including some presented at a WHO meeting in mid-December, confirmed earlier findings showing that two doses of an mRNA vaccine (Pfizer/BioNTech or Moderna are the mRNA vaccines available in the US) are much less effective against Omicron compared to the earlier coronavirus variant. One small laboratory study conducted by researchers in South Africa, for example, found a 41-fold decrease in neutralization (the ability of antibodies to prevent the virus from infecting cells) with Omicron compared to the earlier coronavirus variant. However, Omicron did not completely evade the immune response. Pfizer/BioNTech also released data from a laboratory study showing a significantly decreased antibody response to Omicron after two vaccine doses.
Neutralization studies, like these, speak largely to the risk of infection. And the results so far suggest that Omicron could lead to more breakthrough infections (in people who are vaccinated) and reinfections (in people who were previously infected).
This is not a surprise. Current vaccines generate antibodies that recognize and respond to the virus’s spike protein. The Omicron variant contains many mutations on its spike protein, making it more difficult for antibodies to recognize.
More promising findings from Pfizer/BioNTech showed that after three vaccine doses (two doses plus a booster), the neutralizing antibody response was comparable to the strong immune response to an earlier version of the virus seen after two vaccine doses. Preliminary research from the National Institute of Allergy and Infectious Disease’s Vaccine Research Center, conducted in the lab using the Moderna vaccine, similarly showed that boosters increase antibody-derived protection.
The benefit of boosters is also being seen in the real world. In one pre-print study, researchers in the United Kingdom, where Omicron cases are rising, showed that protection against infection and mild disease increased from about 40% four months after two Pfizer/BioNTech shots to about 75% within two weeks after a booster dose.
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. In the Pfizer/BioNTech study, a booster dose strongly increased levels of a certain type of T cell. This should provide additional protection. And a laboratory study from South Africa found that the T cell response to Omicron is largely preserved compared to older variants. Our immune system, especially when boosted by vaccination, is complex, powerful, and adaptive.
For all that we are learning about Omicron, the take-home messages remain the same. 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.
Which COVID-19 vaccines are available for children?
The CDC recommends that children ages 5 to 17 years receive a Pfizer/BioNTech COVID-19 vaccine. Children 12 to 17 years may be vaccinated with the standard Pfizer/BioNTech vaccine, while children ages 5 to 11 years should receive Pfizer/BioNTech’s pediatric vaccine, which is a lower dose (10 micrograms, compared to 30 micrograms for people 12 year and older). For now, only the Pfizer/BioNTech vaccine is authorized in the US for anyone under age 18.
The CDC also recommends a single-dose Pfizer/BioNTech COVID-19 booster shot for children ages 12 to 17 years, at least five months after getting their second dose of that vaccine.
In addition, the CDC advises that children ages 5 years and older who are moderately to severely immunocompromised should get an additional primary dose of the vaccine 28 days after their second shot.
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 are monoclonal antibodies? Can they help treat COVID-19?
Monoclonal antibodies are manmade versions of the antibodies that our bodies naturally make to fight invaders, such as the SARS-CoV-2 virus. Three monoclonal antibody treatments for COVID-19 have been granted emergency use authorization (EUA) by the FDA. The 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. These therapies must be given intravenously (by IV) soon after developing symptoms.
The monoclonal antibody treatments that have EUA approval are:
- a combination of casirivimab and imdevimab, called REGN-COV, made by Regeneron
- a combination of bamlanivimab and etesevimab, made by Eli Lilly
- sotrovimab, made by GlaxoSmithKline.
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. This has translated into a disadvantage when it comes to fighting the Omicron variant, which has more than 30 mutations on its spike protein. Laboratory studies have found that only one of the FDA-authorized monoclonal antibody treatments — sotrovimab — is effective against Omicron.
As of January 2022, the number of patients who would benefit from monoclonal antibody treatment far exceeds the supply and the infrastructure to deliver this therapy. Once oral antiviral medications are more available, there will be more treatment options for high-risk patients.
Monoclonal antibody treatment may also help to save lives in a specific subgroup of hospitalized COVID-19 patients. Some COVID patients get sicker because of an overreaction of the body’s immune response (a cytokine storm) to the viral infection. When this happens, the body overproduces interleukin-6 (IL-6) — a protein involved in inflammation — in lung cells. For these very ill hospitalized patients, the FDA has granted EUA for tocilizumab (Actemra), a monoclonal antibody that blocks the action of IL-6, and thereby dampens the exaggerated immune system response.
What needs to happen for schools to remain open and for children to remain safely in school?
School closures have impacted children on many fronts, from academics and social interaction to equity, food security, and mental health. Keeping children safely in school is a priority for the CDC.
In December 2021, in order to further minimize disruptions to school attendance and learning, the CDC endorsed "test to stay." This is a strategy through which children who are close contacts of someone who tests positive for COVID-19 can remain in school — masked — if they test negative twice during the week after they were exposed. (Children who develop symptoms or test positive should isolate at home.) The CDC’s endorsement was based on two reports published in MMWR. One report from California and another report from Illinois showed that test to stay can limit in-school transmission of COVID while preserving in-person learning.
The CDC recommends that all teachers, staff, students, and visitors to schools wear masks while indoors, regardless of whether or not they are vaccinated. They also recommend that everyone who is eligible for vaccination get the vaccine.
Vaccination, masking, and test to stay are three of several prevention strategies that, when layered together, help to minimize the spread of COVID-19 in schools. Other prevention strategies include physical distancing; screening, testing, and contact tracing; staying home when sick; and frequent handwashing. Schools should also do their best to improve ventilation, by opening windows and doors, for example. Decisions about some of these prevention strategies may depend on levels of community transmission.
I've tested positive for COVID-19. How long do I need to isolate?
The most recent CDC guidance states that everyone who tests positive for COVID-19 should
- isolate at home for five days
- if you have no symptoms or your symptoms are improving after five days, you can discontinue isolation and leave your home
- continue to wear a mask around others for five additional days.
If you have a fever, continue to isolate at home until you no longer have a fever.
Although not yet officially recommended by the CDC, consider having a rapid COVID test at the end of five days to determine if you should continue to isolate.
I was recently exposed to someone who tested positive for COVID-19. When can I discontinue my self-quarantine?
Whether and for how long you need to quarantine depends on you vaccination status, according to the latest guidance from the CDC.
If you have been boosted OR had your first two Moderna or Pfizer shots within the last six months OR got a Johnson & Johnson vaccine within the last two months, you do not need to quarantine if you’ve been exposed to someone with COVID-19. However, you should
- wear a mask around others for 10 days
- test on day 5, if possible.
If you develop symptoms, get tested and isolate at home.
If you had your first two Moderna or Pfizer shots more than six months ago and are not boosted OR got a Johnson & Johnson vaccine more than two months ago and are not boosted OR are unvaccinated:
- Quarantine at home for five days. After that, continue to wear a mask around others for five more days.
- If you can’t quarantine, wear a well-fitting mask around others for 10 days.
- Test on day 5, if possible.
If you develop symptoms, get tested and isolate at home.
Is there an antiviral pill that can reduce my risk of being hospitalized if I get COVID-19?
The FDA has authorized two antiviral pills for the treatment of COVID-19.
On December 22, 2021, the FDA authorized an oral antiviral pill, called Paxlovid, for the treatment of mild-to-moderate COVID-19 in people ages 12 and older who are at increased risk for severe illness. The treatment is available by prescription only, after a positive COVID-19 test and within five days of symptom onset. The FDA’s authorization was based on study results released by Pfizer, the drug’s manufacturer, showing that Paxlovid significantly reduces the risk of COVID-related hospitalization and death compared to a placebo.
The phase 2/3 study, known as EPIC-HR, 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. The 2,246 study participants took either a placebo or Paxlovid treatment (three tablets twice a day for five days), beginning treatment within five days of symptom onset.
By 28 days after treatment, those who had taken Paxlovid within five days of the start of symptoms had an 88% reduced risk of COVID-related hospitalization or death compared to placebo. Side effects of Paxlovid and placebo were comparable, and generally mild. They included impaired sense of taste, diarrhea, high blood pressure, and muscle aches.
Paxlovid is a protease inhibitor antiviral therapy made up of a medicine called nirmatrelvir and the HIV drug ritonavir. Nirmatrelvir was developed by Pfizer; it interferes with the ability of the coronavirus to replicate. Ritonavir slows the breakdown of nirmatrelvir, which translates to higher blood levels of nirmatrelvir and greater antiviral action for longer periods of time.
Laboratory study results, also announced in a Pfizer press release, suggest that Paxlovid is effective against the Omicron variant.
Paxlovid is not authorized to prevent infection, to prevent illness after exposure (prior to diagnosis), or to treat someone hospitalized with severe COVID-19. Antiviral medication is also not a substitute for getting vaccinated. The COVID vaccine, including boosters, remains more important than ever. We need layers of defense against this viral threat.
On December 23, 2021, the FDA authorized molnupiravir, an oral antiviral treatment manufactured by Merck, for the treatment of mild to moderate COVID-19 in people ages 18 years and older who are at increased risk for severe illness. The treatment is available by prescription only, after a positive COVID-19 test and within five days of symptom onset. However, the FDA indicated that use of molnupiravir should be limited to situations in which other COVID-19 treatments "are not accessible or clinically appropriate."
In November, Merck released study results showing that compared to placebo, molnupiravir reduced the risk of hospitalization and death by 30% in people with mild or moderate COVID-19 who were at high risk for severe COVID.
The study results were based on data from 1,433 study participants from the US and around the world. To be eligible for the randomized, placebo-controlled, double-blind 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 30% less likely to be hospitalized or die from COVID-19 than those taking a placebo. Over the 29-day study period, 48 out of 709 (6.8%) of participants who took molnupiravir were hospitalized, and one person in this group died. In the placebo group, 68 out of 699 (9.7%) of participants were hospitalized, including nine participants in this group who died. The antiviral drug was effective against several COVID variants, including the Delta variant. Scientists are looking into the effectiveness of molnupiravir against the Omicron variant.
Side effects of molnupiravir include diarrhea, nausea, and dizziness. The drug is not recommended for use during pregnancy.
Molnupiravir was developed by Merck and Ridgeback Biotherapeutics. It works by interfering with the COVID virus’s ability to replicate.
- 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
- Did we really gain weight during the pandemic?
- Wondering about COVID-19 vaccines if you're breastfeeding?
- 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!