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Coronavirus Resource Center

July 28, 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

What is the connection between the Johnson & Johnson COVID-19 vaccine and Guillain-Barré syndrome?

In July 2021, the FDA warned that the Johnson & Johnson (J&J) COVID-19 vaccine may lead to a small but increased risk of Guillain-Barré syndrome (GBS). GBS is a disorder in which the body destroys its own nerve cells. It can lead to muscle weakness and sometimes paralysis, trouble breathing, or, rarely, death. The risk of developing GBS after receiving the J&J vaccine is very low, and benefits of vaccination still far outweigh the risks.

The FDA’s warning was based on preliminary reports of about 100 cases of GBS that occurred in people who had received the J&J vaccine. To date, about 12.8 million people in the US have gotten the J&J vaccine. Most of the reported cases occurred in men ages 50 years and older, about two weeks after vaccination.

Almost all required hospitalization because GBS can affect the nerves to chest muscles and the diaphragm, making it difficult to breathe. Most people recover completely from GBS within a few months, but some never regain full strength.

Seek immediate medical attention if you experience any of the following symptoms after receiving the J&J COVID-19 vaccine:

  • weakness or tingling sensations, especially in the legs or arms, that’s worsening and spreading to other parts of the body
  • difficulty walking
  • difficulty with facial movement, including speaking, chewing, or swallowing
  • double vision or inability to move eyes
  • difficulty with bladder control or bowel function.

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

Mutations have led to several new, concerning coronavirus variants, including the B.1.1.7 (Alpha) variant, which was first detected in the United Kingdom; the B.1.351 (Beta) variant, which originated in South Africa; the P.1 (Gamma) variant, which originated in Brazil, and the B.1.617.2 (Delta) variant, which was first documented in India. Emerging evidence suggests that the current vaccines are effective against at least some of these variants.

Two peer-reviewed and published studies have found the Pfizer/BioNTech vaccine to be extremely effective against the Alpha and the Beta variants. The first study, published in NEJM, looked at data from more than 200,000 people from the country of Qatar between early February and late March 2021. During that time, the Alpha and Beta variants were responsible for nearly all COVID cases in that country. The researchers found that in people who were fully vaccinated, the Pfizer vaccine was 97.4% effective at preventing severe, critical, or fatal disease caused by the Alpha or Beta variants.

The second study, published in The Lancet, looked at more than 200,000 COVID infections in Israel from late January to early April 2021, when the Alpha variant accounted for more than 90% of infections. The researchers found that in fully vaccinated people, the Pfizer vaccine was nearly 97% or more effective at preventing symptomatic COVID-19, COVID-related hospitalization, severe or critical COVID-19, or COVID-related death.

Newer research has also found the Pfizer/BioNTech vaccine to be effective against the Delta variant, which is now the dominant variant in the US. A study from Public Health England found that full vaccination with the Pfizer/BioNTech vaccine was 88% effective at protecting against symptomatic illness caused by the Delta variant, and 96% effective at preventing hospitalization due to the Delta variant.

Studies on the effectiveness of the Moderna vaccine are ongoing. In the lab, it has performed well against the Alpha variant, compared to the original, unmutated virus. However, it was less effective against the Beta and Delta variants compared to the unmutated virus and the Alpha variant. More study is needed to see if the laboratory results hold up in real-world conditions.

It's important to remember that both the Pfizer/BioNTech and Moderna vaccines are extremely effective — 95% and 94.1%, respectively. Even with some possible decrease in effectiveness against variants, they will still provide excellent protection against severe illness.

Another study, published in Nature, looked at blood samples from people who received the Johnson & Johnson adenovirus vaccine. It found that the vaccine produced a less robust antibody response against the Beta and Gamma variants compared to the response to the original SARS-CoV-2 virus. However, the T cell immune response held up, particularly among the type of T cells that prevent the virus from spreading within the body. This immune response should protect against developing severe symptoms if a person does get infected. Johnson & Johnson also released data from a small, unpublished laboratory study, which found a strong neutralizing antibody response against the Delta variant in people who had received the single-shot J&J vaccine. The response was sustained for at least eight months, the duration of the study.

I have been hearing about heart problems in kids and young adults following the COVID vaccine. Should I still get my child vaccinated?

There has a been a higher-than-expected number of heart inflammation cases after vaccination with the mRNA COVID-19 vaccines, particularly among boys and young men. However, the CDC still strongly recommends that all children 12 years and older be vaccinated.

As of July 12, 2021, 1,047 reports of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart) had been reported in people under age 30, particularly in male teens and young adults, after vaccination with the Pfizer/BioNTech or Moderna mRNA vaccines The CDC’s Advisory Committee on Immunization Practices (ACIP) has said available data "suggest likely association of myocarditis with mRNA vaccination in adolescents and young adults." Even with the increased risk, heart inflammation is a rare occurrence.

Myocarditis and pericarditis after vaccination was most common in males ages 16 to 24. Cases tended to occur within several days after the second mRNA vaccine dose. Most people who developed myocarditis or pericarditis had mild cases and recovered completely after treatment.

If your child develops any of the following symptoms within a week of vaccination, seek medical care:

  • chest pain
  • shortness of breath
  • feeling like your heart is beating fast, fluttering, or pounding.

This or any other potential significant side effect of a vaccine is always of special concern in children. While the risk of COVID causing severe illness and hospitalization is much lower compared to adults, it’s important to remember that at least 491 children ages 0 to 17 years have died from COVID. In addition, long-term adverse health effects even after mild infection in children are now being recognized.

It’s understandable that many parents will be uncomfortable with either choice, vaccinate now or wait. But the rise of the more contagious and possibly more dangerous Delta variant, combined with the protection offered by herd immunity, supports the CDC recommendation that all children ages 12 year and older get vaccinated.

What do we know about the Novavax COVID-19 vaccine?

The Novavax COVID-19 vaccine appears to be effective and safe, according to an analysis of phase 3 trials results released by the company in a press release. The trial found the vaccine to be 90% effective overall, and 100% effective against moderate and severe disease. The vaccine requires two doses, given three weeks apart, and may be stored using standard refrigeration.

The PREVENT-19 trial enrolled 29,960 participants, ages 18 years and older, across the US and Mexico. Two-thirds of the participants received the Novavax vaccine and one third received a placebo. The trial was randomized, and observer-blinded, meaning the study participants and those evaluating the study endpoints did not know which participants received the vaccine.

Between January 25 and April 30, 2021, there were 77 confirmed cases of COVID-19 among the study participants. Of these, 63 occurred in the placebo group and 14 occurred in the vaccine group. All of the cases that occurred in the vaccine group were mild. Of those that occurred in the placebo group, 10 were moderate and four were severe. This translated to 100% efficacy against moderate and severe disease. The vaccine was 91% effective in people at high risk, which the study defined as people 65 years or older, with a medical condition that increased risk of severe COVID illness, or whose jobs increased their risk of exposure to COVID-19.

Side effects from the vaccine included arm pain at the injection site, fatigue, headache, and muscle pain.

The Novavax vaccine is a recombinant protein vaccine. Similar to COVID vaccines that are already available in the US, it stimulates the body to produce antibodies against the spike protein found on the outer surface of the SARS-CoV-2 virus. The Novavax vaccine contains spike protein produced in a laboratory along with an adjuvant to boost the human immune response.

The vaccine is already being tested in adolescents ages 12 to 17.

Which COVID-19 vaccines has the FDA authorized for children?

On May 10, 2021, the FDA expanded its emergency use authorization (EUA) for the Pfizer/BioNTech COVID-19 vaccine to include adolescents 12 to 15 years old. Previously, the Pfizer vaccine was authorized for use in children 16 years and older. For now, this is the only vaccine authorized in the U.S. for anyone under age 18.

Pfizer has been conducting age de-escalation studies, in which its vaccine is tested in groups of children of descending age. The EUA’s expanded authorization was based on results from a Phase 3 trial of children ages 12 to 15. The trial enrolled 2,260 adolescents; half received the Pfizer mRNA vaccine, the other received a saltwater placebo.

The immune response in the vaccinated adolescent group was even stronger than that in vaccinated 16- to 25-year-olds enrolled in an earlier study. In addition, a total of 16 symptomatic cases of COVID-19 were reported during the trial, all in the placebo group, which meant that the vaccine had been 100% effective in preventing COVID-19.

Vaccine-related side effects were mild and included pain at the injection site, tiredness, headache, chills, muscle pain, fever, and joint pain. Pfizer has also started testing the vaccine in children younger than 12 years.

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

New research suggests that people who have already gotten sick with COVID-19 benefit from the vaccine, possibly even more than vaccinated people who were not previously infected.

A study published in NEJM found that people who were previously infected with SARS-CoV-2 and then received a single dose of either mRNA vaccine (Pfizer/BioNTech or Moderna) experienced a rapid immune response and generated at least as many, or more, antibodies as previously uninfected people who had received two doses of vaccine.

And a study published in Science compared the effects of the Pfizer vaccine in people with and without prior infection. The researchers found that previously infected people who were vaccinated had a stronger immune response against the B.1.1.7 and B.1.351 variants than previously uninfected people who were vaccinated.

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

Why is the CDC asking fully vaccinated people to wear masks again? Where and when do I need to wear a mask now?

In July 2021, the CDC advised all people — vaccinated and unvaccinated — to wear masks in public indoor places, in areas with substantial or high transmission of the virus. The CDC has always advised unvaccinated people to mask indoors, and also advises anyone at increased risk to wear a mask indoors, regardless of the level of community transmission. The change in guidance for people who are fully vaccinated was made amidst increasing numbers of infections and hospitalizations across the country.

One factor driving increased infections is the rise of the Delta variant, which spreads more easily than other variants. The Delta variant is now the dominant variant in the US.

We know that people who are fully vaccinated have a much smaller risk of getting sick if they are exposed the Delta variant. While they are also less likely to spread the virus, the Delta variant is more capable than the original virus of getting into cells that line the nose, mouth, and throat. Once these variants get inside the cells, they rapidly make copies of themselves, increasing what is called the viral load. That’s why people who are fully vaccinated can still carry greater amounts of the Delta variant, making it more likely that they could spread the virus to others.

This is where the new masking guidelines come in. Masks reduce the amount of virus we breathe in, and breathe out. Combined with the vaccine, masks provide a one-two punch that reduces the risk of spread — to children who are not yet eligible for vaccines, to people with weakened immune systems, and to others who are unvaccinated.

Masks also provide additional protection for the wearer, even those who are fully vaccinated. Vaccines have been very effective, even against the Delta variant, in protecting against severe infection, hospitalization, and death. However, the Delta variant has led to a number of breakthrough infections in people who are fully vaccinated, and masks provide another layer of protection.

To check the level of virus transmission in your area, visit the CDC’s COVID Data Tracker. Areas with substantial or high transmission appear in orange or red.

What is the new naming system for COVID-19 variants?

The WHO recently announced a new naming system for COVID-19 variants. The new names are intended to be easier to pronounce and will remove the stigma of a variant’s being associated with a particular country.

Under the new system, the variants will be named using letters of the Greek alphabet. For example:

  • Alpha is the new name for the B.1.1.7 variant, first documented in the United Kingdom.
  • Beta is the new name for the B.1.351 variant, first documented in South Africa.
  • The P.1 variant, first documented in Brazil, will now be known as Gamma.
  • The B.1.617.2 variant, first documented in India, will be called Delta.

For a complete list of new SARS-CoV-2 variant names, click here.

Scientists will likely continue referring to variants by strings of letters and numbers, which provide information about a variant’s lineage.

What are breakthrough infections, and why do they happen?

A breakthrough infection is one that occurs after full vaccination.

In an article published in MMWR, the CDC reported 10,262 breakthrough infections through the end of April 2021. By that point, more than 100 million Americans had received the COVID-19 vaccine.

The vast majority of breakthrough infections were asymptomatic, mild, or moderate. About 1,000 people with breakthrough infections were hospitalized, and 160 died, though the hospitalizations and deaths were not always related to COVID-19.

These numbers tell us that the vaccines are doing a good job preventing infection and severe illness. None of the vaccines were 100% effective in clinical trials, so a small number of breakthrough infections was expected.

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

Mutations have led to at least four concerning coronavirus variants. One, called Alpha, or B.1.1.7, was first detected in the United Kingdom. Another, called Beta, or B.1.351, originated in South Africa. A third, called Gamma, or P.1, originated in Brazil. And a fourth, called Delta, or B.1.617.2, was first documented in India. All four variants have now been detected in countries around the globe.

All of these variants contain mutations on the virus's spike protein. Spike proteins on the surface of the SARS-CoV-2 virus bind to and allow the virus to enter human cells. The Alpha, Beta, and Gamma variants share a key mutation (called N501Y) on the spike protein, which allows the virus to bind more tightly to human cells. This mutation makes the new variants more contagious than previous SARS-CoV-2 variants. The Beta and Gamma variants also share a second mutation, called E484K, which might make it easier for them to re-infect someone who has already been infected or, possibly, someone who has been vaccinated.

The B.1.1.7 (Alpha) variant is estimated to be about 50% more transmissible than previous SARS-CoV-2 variants. On April 7, 2021, the CDC announced that B.1.1.7 is now the most common variant circulating in the US. There are conflicting reports about whether this variant is more virulent; two published studies found that the B.1.1.7 variant is associated with a 55% to 64% greater chance of severe illness and death, but another study, published in The Lancet, did not find this variant to be associated with an increased risk of severe disease or death. Two peer-reviewed studies published in May 2021 found the Pfizer/BioNTech vaccine to be extremely effective against the B.1.1.7 and the B.1.351 variants.

The Delta, or B.1.617.2, variant is now the dominant variant in the United States. The CDC has classified it as a variant of concern. The Delta variant is highly transmissible, and there is some evidence that it is associated with increased disease severity. However, a study from Public Health England found that full vaccination with the Pfizer/BioNTech vaccine was 88% effective against this variant.

The emergence of these more transmissible and virulent variants is yet another reason why getting vaccinated once you are eligible and following CDC guidance on prevention measures continue to be as important as ever.

I had COVID-19 a few months ago. Am I at increased risk for health problems in the future?

It does appear that people who recover from COVID-19 have an increased risk of developing other medical conditions, at least in the short term.

One study, published in The BMJ, collected laboratory test and hospital admissions data from a health plan in the US. The researchers compared data from more than 190,000 adults, ages 18 to 65 years, who tested positive for the SARS-CoV-2 virus in 2020, to data from a control group that was collected in 2019, before the pandemic. The researchers followed the participants for six months after they tested positive for SARS-CoV-2 and recorded any new health complications.

They found that 14% of people who had had COVID-19 developed a new medical issue during the following six months; this was nearly 5% higher than the pre-pandemic control group, a significant difference. New medical problems affected a range of body systems and included respiratory failure, abnormal heart rhythms, diabetes, neurological problems, and liver and kidney problems. Increased risk was seen in younger, previously healthy people, but was higher in older people and those with pre-existing medical problems.

Another study, published in Nature, compared the health records of more than 73,000 users of the Veteran’s Health Administration (VHA) who tested positive for SARS-CoV-2 but were never hospitalized, to those of nearly five million other VHA users who never tested positive for COVID-19 and were never hospitalized. For six months following the first 30 days after infection, people who had had COVID-19 were significantly more likely to die or to experience a medical or mental health problem that they had never had before.

These studies provide yet another reason to get a COVID-19 vaccine if you are eligible.

What outdoor and indoor activities are considered safe? Does it matter if I’ve been vaccinated? And do I still need to wear a mask?

According to new guidance from the CDC, fully vaccinated people can now participate in all indoor and outdoor activities without a mask and without physical distancing. For people who are not fully vaccinated, the CDC continues to recommend mask wearing and other preventive measures in some outdoor settings and in most indoor settings.

If you have a weakened immune system due to a medical condition or to medications you are taking, you may be less protected by the vaccine and thus at increased risk when you are around others who have not been vaccinated. Talk to your doctor to find out what safety measures you should continue to take.

Whether you’re vaccinated or not, you’ll need to follow federal, state, tribal, and local laws, and workplace or business requirements around mask wearing and physical distancing.

The CDC has created a helpful chart illustrating the protection vaccination provides in all outdoor and indoor activities, and what prevention measures you still need to take if you are not vaccinated. To view the chart, click here.


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.

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


Questions?

Harvard Health Publishing Coronavirus Resource Center Experts

The Harvard Health Publishing team would like to acknowledge the Harvard Medical School experts who have contributed their time and expertise: Steven A. Adelman, 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, MDRobert 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.

Disclaimer:

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.