What You Need to Know about Coronavirus (COVID-19)

Diana Zuckerman, Ph.D. & Thomas Eagen, Ph.D. Updated November 19, 2021

The coronavirus can infect anyone, young or old, healthy or frail. Here’s what you need to know.

What is coronavirus?

Coronaviruses are a large group of viruses that can cause respiratory illness. The new (novel) coronavirus is called SARS-CoV-2 and the illness it causes is called coronavirus disease 2019, which is why it’s abbreviated as COVID-19. This virus is highly contagious and deadly with over 200 million confirmed cases and over 4.5 million deaths globally. As of August 31, 2021 there have been 38 million confirmed cases in the U.S. and over 600,000 deaths. 

Who is at risk of severe illness from COVID-19?

Older adults or people who have cancer and other serious health conditions are at increased risk for getting seriously ill from COVID-19. These individuals and their loved ones need to be especially careful to avoid getting infected and potentially hospitalized. The Centers for Disease Control and Prevention (CDC) has a list of health problems that put people at greatest risk of severe illness from COVID-19, which include underlying medical conditions such as: chronic kidney disease, chronic obstructive pulmonary disease (COPD), obesity (body mass index of 30 or higher), weakened immune system (from cancer or an organ transplant), serious heart conditions, sickle cell disease, and Type 2 diabetes. This risk has been shown to increase with age. Smoking also increases the risk of being seriously harmed by the virus. 

A study published in the Journal of the American Heart Association found that two-thirds of COVID-19 hospitalizations can be attributed to four cardiometabolic conditions: obesity, high blood pressure, diabetes, and heart failure. Many other medical conditions might contribute to an increased risk of severe illness, including asthma, developmental disabilities, high blood pressure, neurologic conditions (e.g., dementia), cerebrovascular disease (e.g., stroke), and pregnancy. Another study published in the Journal of the American Medical Association (JAMA) Oncology in December 2020 of more than 6 million cancer patients, found that people diagnosed with cancer during the previous year are much more likely to die of COVID-19 compared to other COVID-19 patients. All cancer patients were at higher risk, but the ones in most danger had been diagnosed with leukemia, non-Hodgkin’s lymphoma, or lung cancer.

How does COVID-19 spread between people?

The virus usually spreads through close contact with other people, especially through invisible or very tiny droplets when a person coughs, sneezes, sings, exercises – or even when they breathe or talk normally. These droplets can travel through the air and can be inhaled or get into the noses, mouths, or eyes of people nearby.

The virus is thought to be most contagious in the days just before and just after a person develops symptoms, but it is possible to catch the virus from infected people who have no symptoms at all. Becoming infected by exposure to people with no symptoms may be especially likely with the Delta variant, or if the asymptomatic person was vaccinated.       

Unlike the flu, which is riskiest for the youngest children and oldest adults, infants and young children are much less likely to get seriously ill from the coronavirus than adults. Preliminary studies suggest that children over 10 are as contagious as adults, but that younger children are much less infectious. For example, there are few known examples of the virus spreading in daycare centers that follow coronavirus safety standards. Nevertheless, by August 26, 2021 nearly 4.8 million children had been diagnosed with the virus in the U.S. This represents over 14% of total cases, and this number had increased over the previous two months. Fortunately, few children become so sick that they are hospitalized (estimates range from less than 1% to 8.5%), and less than half of 1% of children diagnosed with coronavirus in the U.S. have died.

If I’ve had COVID-19, am I immune in the future?

A large Danish study of almost 4 million individuals (nearly 70% of the Danish population)  found that having previously been infected by the COVID-19 virus provides protection against a repeated infection, particularly for people younger than 65 years. However, it is clear that people who previously had COVID-19 can become infected months later, and the strength and duration of immunity remain unclear. 

Do we know how the virus is changing?

It is normal for viruses in the environment to change or mutate, resulting in new variants of the same virus. This is why the CDC recommends that adults and children receive a seasonal flu shot – to strengthen the body’s immune response against the variant with the potential to spread throughout a community. Many variants of the COVID-19 virus have emerged globally during the pandemic. The U.S. government is routinely monitoring for variants of concern that may show: 

  • Evidence of impact on diagnostics, treatments, or vaccines
    • Widespread interference with diagnostic test targets
    • Evidence of substantially decreased susceptibility to one or more class of therapies
    • Evidence of significant decreased neutralization by antibodies generated during previous infection or vaccination
    • Evidence of reduced vaccine-induced protection from severe disease
  • Evidence of increased transmissibility
  • Evidence of increased disease severity

The Delta variant, which was first identified in December 2020 in India, has been shown to be more contagious than the other virus strains and has quickly become the most dominant strain of COVID-19 globally. Some data reported by the CDC suggest the Delta variant is more than twice as contagious and may cause more severe illness. In two different studies from Canada and Scotland, patients infected with the Delta variant were more likely to be hospitalized than patients infected with the original virus. 

What about the vaccines?

The COVID-19 vaccines that have been authorized or approved in the U.S. are designed to prevent serious illness, hospitalization, and death due to the virus. They are not 100% effective and some people who are fully vaccinated have become infected, called a breakthrough infection. These individuals have usually experienced mild illness, but some have become seriously ill.

On August 23, 2021, the Food and Drug Administration (FDA) approved the first COVID-19 vaccine, which is called Comirnaty, for the prevention of COVID-19 disease in individuals 16 years of age and older. This vaccine is made by Pfizer-BioNTech using mRNA technology, and it currently requires two doses separated by 21 days. The two-dose series of the vaccine is also available under emergency use authorization (EUA) for individuals 5 years or older. A three-dose series is authorized for those 12 years or older who are immunocompromised, and anyone ages 18 and older can get a third “booster” dose. Booster doses are discussed in more detail below.

Two other vaccines are currently available in the U.S. under EUA, one produced by Moderna, which requires two doses using mRNA technology, and one produced by Johnson & Johnson, which requires a single dose using an adenovirus.

As of November 18, 2021 approximately 446 million doses of these three vaccines have been given in the U.S., with 59% of the entire U.S. population fully vaccinated. Rates of vaccination differ greatly by state and demographics.

All three vaccines have been shown to be safe and effective at preventing serious illness from COVID-19. Studies have found the Pfizer or Moderna vaccines to be slightly more effective than the Johnson & Johnson vaccine. Keep in mind, however, that the vaccines were not studied on any nursing home patients and not studied on many individuals who were ages 65 or older who were exposed to the virus, so they might be less effective for older people. The initial studies of the three vaccines included few people under 18, pregnant women, people with compromised immune systems, or those with serious allergies; however, a study published in May 2021 in JAMA indicated that the vaccine is generally safe for these individuals. Research has found the vaccines to be less effective on people with compromised immune systems, such as those with organ transplants that take drugs to prevent organ rejection.

The duration of immunity from the vaccines remains unclear. In October 2021, a third primary dose of the Pfizer-BioNTech and Moderna vaccines was authorized under the FDA EUA for individuals who are immunocompromised to be administered six months after the second dose. The initial effectiveness studies followed participants for a median of 2 months and well-controlled data are lacking as to how long the vaccines last and for whom. As of November 19, 2021, booster doses are authorized for all adults 18 and older at least 6 months after their second dose. Although available for all adults, the CDC specifically recommends the booster for adults ages 50 and older. The booster dose of the Moderna vaccine is 1/2 the dose of the primary 2 doses. The CDC also recommends that those 18 and older who received the Johnson & Johnson vaccine at least 2 months ago should get a booster shot.

The FDA has also authorized “mixing and matching” vaccines for booster doses. For example, someone who got the Johnson & Johnson vaccine could get a booster dose of the Moderna (half dose) or Pfizer-BioNTech vaccines at least 2 months after their initial dose, or someone who got both primary doses of the Moderna vaccine could get a booster dose of the Pfizer-BioNTech vaccine 6 months after completing their 2 doses of Moderna.

Common side effects from the vaccines include: pain, redness, and swelling on the arm where you receive the shot; and tiredness, headache, muscle pain, chills, fever, and nausea throughout the rest of your body. Effects are typically stronger following the second dose of Pfizer or Moderna. In April 2021, there was a temporary pause to the use of the Johnson & Johnson vaccine after reports of rare blood clots with low platelets, which have largely occurred in adult women younger than 50 years old. Following a review of the data, the FDA added a warning label to the vaccine about the uncommon blood clotting disorder. The side effects outweigh the potentially severe effects of COVID-19 and should not dissuade most adults from getting vaccinated. One study found a 16 times higher risk of myocarditis (i.e., inflammation of part of the heart muscle) among patients with COVID-19 compared to those without. It is important that anyone getting vaccinated is told about potential risks, since they could be frightening to patients who don’t understand that those symptoms are not thought to be reason for concern.

What are the symptoms of COVID-19?

Symptoms tend to start between 2 and 14 days after coming into contact with the virus. Although some people have compared the symptoms to a cold or flu, not everyone with COVID-19 has those types of symptoms. In fact, some people (especially children, teens, and younger adults) have very mild symptoms or none at all, which is why getting tested is so important before you spend time with others. These symptoms have been reported in people with COVID-19:

  • Fever or chills 
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Muscle pains
  • Headache
  • New loss of taste or smell
  • Sudden confusion (delirium)
  • Skin rash, redness on toes/fingers
  • Chest pains
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea
  • Skipping meals
  • Abdominal pains
  • Sneezing 
  • Changes in the mouth or tongue

Most people who are infected with this coronavirus have mild symptoms and can recover at home in about 2 weeks. However, symptoms can become severe. These are the ones that require immediate medical attention:

  • Difficulty breathing or shortness of breath
  • Persistent chest pain or pressure
  • Confusion or inability to awaken
  • Blueish color in the lips or face

As described above, people who are older than 60 or with other medical conditions are more likely to develop severe illness and complications from COVID-19. The most serious complications include pneumonia, stroke, blood clots, organ failure, and death.

How can I protect myself and others?

If you live in the U.S., the best way to protect yourself and others it to get one of the 3 vaccines available. The vaccines are widely available throughout the U.S. in multiple locations from community health centers to local pharmacies. Current treatment options for COVID-19 are limited. There are no proven cures, so don’t be fooled by claims, regardless of the source. The FDA has approved one drug treatment for COVID-19 and has granted EUAs for 11 drug treatments.  

The FDA approved the antiviral drug remdesivir, which has been found to help very ill adults and children 12 years of age or older reduce the number of days of hospitalization. In one study sponsored by the National Institute of Allergy and Infectious Diseases showed a significantly faster time to recovery in patients taking remdesivir (about 10 days) compared to the placebo group (about 15 days). 

The FDA has authorized several monoclonal antibody treatments for individuals with mild to moderate illness due to COVID-19. This treatment has been shown to reduce the risk of illness progressing to severe illness, including hospitalization or death. A different monoclonal antibody has been authorized to prevent COVID for individuals who were exposed. Monoclonal antibodies are laboratory-made proteins that mimic the immune system’s ability to fight off harmful antigens such as viruses.  

Experts now agree that hydroxychloroquine with or without azithromycin is not a good treatment for COVID-19 because it has been found to increase heart problems and has not been shown to prevent or treat COVID-19. 

Another possible treatment is blood plasma from people who recovered from COVID-19. Known as convalescent plasma, this blood product contains antibodies that help fight the virus. Convalescent plasma currently has emergency FDA authorization for treating hospitalized COVID-19 patients early in the disease course. However, studies published in the summer of 2021 indicated that this treatment was not effective.      

Ivermectin is a drug approved by the FDA for human use to treat infections caused by internal and external parasites, but it has not been approved to treat COVID-19. A study suggested ivermectin may inhibit COVID-19 cells in laboratory studies, however data showing efficacy against COVID-19 in people is lacking. Despite the lack of data showing effectiveness, the drug has gained popularity as a potential treatment to the virus. This is concerning because ivermectin can have dangerous side-effects. Calls to poison control centers due to ivermectin ingestion have increased five-fold from their pre-pandemic baseline, leading the CDC to issue an emergency health advisory. Several organizations have issued public statements against the use of ivermectin as a treatment to COVID-19 including the National Institutes of Health (NIH), World Health Organization, FDA, and the American Medical Association (AMA).       

Research is continuing to find out which of these treatments are safe and effective and for which patients.

What else can I do to stay safe?

In addition to getting vaccinated, you may want to change who you spend time with and the types of activities you participate in. 

  • Avoid spending time with others if you or any of them have symptoms of COVID-19 or have been exposed to someone with COVID-19 in the last 14 days.
  • Anyone who has had close contact with a person with COVID-19 should stay home and monitor for symptoms.

In general, the more people you interact with, the more closely you interact with them, and the longer that interaction, the greater your chances of becoming infected or infecting others. Things to consider:

  • How many people will you interact with?  (The fewer the better)
  • Can you keep 6 feet of space between you and others?
  • Will you be outdoors or indoors? (Outdoors is safer if it isn’t crowded. It can be heated, but not if it has walls all around and a ceiling.)
  • What’s the length of time that you will be interacting with people? (Shorter is better)

The CDC recommends all individuals, both vaccinated and unvaccinated, wear a face mask or covering when indoors around others. Research conclusively shows that face masks that cover your mouth and nose help to prevent the spread of the coronavirus. Some masks are more effective than others: stretchy “gators” may actually do more harm than good, and bandanas and scarves are too loose to be very helpful. Paper surgical masks worn in hospitals are effective and so are cloth masks you can make for yourself or buy, if they are made of cotton and at least two layers thick. Masks are important to prevent people from spreading the virus and also to help prevent infection or serious symptoms for the person wearing the masks. 

Other ways to reduce your risk of contracting COVID-19 include:

  • Wash your hands using soap and water for at least 20 seconds, especially after being out in public
  • Use alcohol-based hand sanitizer when soap and water aren’t available (or wash your hands as soon as you get home)
  • Avoid touching your face when your hands aren’t clean or you are out in public
  • Avoid contact with people you don’t know very well
  • Put the toilet seat down before flushing in a shared or public bathroom
  • A lower priority would be to clean and disinfect surfaces including doorknobs, light switches, faucet handles, and phones. An antibacterial cleaning agent won’t kill a virus, so try to find one that is effective for killing viruses.

If you have a weakened immune system or other serious health problems, here are extra steps to protect yourself:

  • Make a plan with your doctor to monitor for symptoms
  • Have a plan with your loved ones or caregiver if you or they get sick
  • Have the medications you rely on and order any you need in advance (to be delivered, if possible)
  • Ask a friend or family member to shop for groceries for you
  • Wash your hands (20 seconds with soap and water) even more often if you are exposed to others

What should I do if I develop symptoms?

If you develop more than one of the symptoms listed above, call your doctor. If you have severe symptoms, such as difficulty breathing, persistent chest pain or pressure, confusion or inability to awaken, or blueish color in the lips or face, you need to call 911. Tell the 911 operator that you think you have COVID-19 so the responders can take the necessary precautions to protect themselves.

People who experience mild symptoms can usually stay home and will recover in about 2 weeks. People are discouraged from simply showing up at the doctor’s office with symptoms: Call them first so you have tell them about your symptoms and any other health problems so that they can help decide what to do. If you do become sick, you can take the following steps to protect others:

  • Get tested for COVID-19, ideally with a PCR test
  • Wear a face mask
  • Stay home, unless you need essential medical care
  • Stay away from others in your home as much as possible
  • Cover your mouth and nose when you cough or sneeze, properly dispose of tissues, and wash your hands
  • Monitor your symptoms and temperature

If you were not tested for COVID-19, you should follow those steps until at least one or two weeks have passed since you first noticed symptoms or your fever or other symptoms go away for 3 full days without medicine. If you have been diagnosed with COVID-19 based on test results, you should follow those same steps until you have 2 negative test results taken 24-hours apart, and your symptoms improve.


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