COVID-19 Testing, At-Home Tests, and What to Know about Isolation and Quarantine

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Swab going into a nose

A nose swab PCR test is one of the most accurate ways to detect COVID-19.

With the recent surge of COVID-19 cases in the United States, many people are concerned about being exposed to the virus and are unsure about what to do if they become infected.

Though the Omicron variant is less severe especially for vaccinated individuals than previous variants of the virus, it is highly contagious, which is cause for concern.

The best way to protect yourself from COVID-19 is to get vaccinated and to get boosted when you are eligible. Today, everyone over age 18 and some people age 12 to 17 can get a booster dose. After you are vaccinated and boosted, you should still wear a mask while in close contact with others, avoid crowded indoor settings, wash your hands often, and be alert for symptoms.

Mini Kamboj

Mini Kamboj

Many of our patients have weakened immune systems because of cancer and its treatment, and they are particularly vulnerable to severe COVID-19. At Memorial Sloan Kettering Cancer Center, we update our COVID-19-related recommendations and policies as often as needed to keep our community safe. This means that sometimes our policies are stricter than the general guidelines from the Centers for Disease Control and Prevention (CDC).

Mini Kamboj, Memorial Sloan Kettering Cancer Center’s Chief Medical Epidemiologist, explains what our patients and their families need to know about COVID-19 testing, quarantining after exposure, and more.

When to Get Tested and Quarantine

I was exposed to someone with COVID-19. Should I get tested?

If you have been exposed to someone with COVID-19 but are not experiencing any symptoms, you should get tested within 2 to 3 days after the exposure. If you do experience symptoms, you should get tested as soon as possible. While you are waiting for results, you should quarantine.

Should members of my household get tested?

Yes. If you have been exposed to someone with COVID-19, the people you live with should follow the same guidelines as above. Remember, Omicron infects faster than previous variants, and most people who develop infection test positive within 3 days of the exposure.

Should I test before getting together with family and friends?

If you are planning to gather indoors with others, you should ensure that everyone around you is fully vaccinated and masked when not eating or drinking. You should do this even if you don’t have symptoms and have not been exposed to someone with COVID-19. If everyone takes a rapid at-home test before gathering, you can have an extra layer of reassurance. 

How long should I quarantine if I was exposed to someone with COVID-19 but I do not have COVID-19 myself?

According to the CDC, there are different recommendations for different groups of people.

If you have been fully vaccinated (including booster shot):

  • You do not need to quarantine, but you should wear a mask for 10 days after the exposure.

If you have not been vaccinated or are partially vaccinated (this includes people who have not received their booster shot and it has been more than 6 months since getting the Pfizer-BioNTech vaccine or more than 2 months since getting the J&J/Janssen vaccine):

  • You should quarantine for 5 days and then wear a well-fitting mask for an additional 5 days when you are around anyone else.

It is important to get tested within 2 to 3 days after the exposure and isolate if you test positive.

Quarantine vs. Isolation

You quarantine if you have been in close contact with someone who has COVID-19.

You isolate when you have COVID-19 yourself, even if you have no symptoms.

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Where to Get Tested

When can I get tested at MSK?

If you are a patient with COVID-19 symptoms and are receiving your cancer care at MSK, you can get tested at any of our testing locations. You can also get tested at an outside location. If you are required to have testing as part of a safety protocol we have implemented — for example, before surgery – you must get tested at MSK.

To get a COVID-19 test at MSK, you must call your doctor’s office to schedule. We do not offer walk-in COVID testing at our clinics.

When and where can I get tested outside MSK?

If you do not have symptoms or any upcoming procedures, you are not able to get tested at MSK. You can find a local testing location using the following links:

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Testing Positive

What do I do if I test positive for COVID-19?

If you test positive for COVID-19, you should isolate yourself at home. This means that you should separate from others, stay in a specific “isolation room” or area, and use a separate bathroom if possible. Don’t share personal household items like cups, towels, and utensils. The CDC has more information on how to isolate safely.

If you have cancer or live with someone who has cancer, you should know that cancer patients are more vulnerable to infection and severe disease. MSK recommends that patients, their close family members, and friends isolate for 10 days — regardless of symptoms — after any positive COVID-19 test.

If you do not have cancer and don’t live with anyone who has cancer or has a weakened immune system, there are different guidelines from the CDC:

  • If you test positive for COVID-19 and have no symptoms, you should isolate yourself for 5 days. After that, you should wear a well-fitting mask for 5 days anytime you are around other people.
  • If you have symptoms, you should isolate for at least 5 days and until your fever goes away for 24 hours (without fever-reducing medicine) and your other symptoms are getting better. Once better, you should wear a well-fitting mask around others for a total of 10 days after your symptoms first appear. If you get hospitalized with COVID-19, you should isolate for at least 10 days and talk to your doctor before ending isolation.

If I test positive for COVID-19, should I get a repeat test at the end of isolation to ensure that I am negative? How long could I test positive for?

The CDC says that if you have access to a test and want to test, you can get a rapid test toward the end of the 5-day isolation period. You should get tested only if you don’t have a fever (without using fever-reducing medicine), and other symptoms have improved. If you test positive again, you should isolate until day 10 after your first positive test. If your test result is now negative, you can stop isolating, but you should wear a mask until day 10 after your first positive test.

PCR (polymerase chain reaction) tests are highly sensitive and considered very accurate at detecting the virus but can stay positive for an extended time, even long after you are no longer contagious. Therefore, they should not be used to decide when you can end isolation.

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Types of Tests

What’s the most accurate test for COVID-19?

PCR tests are the most accurate tests for COVID-19. These tests are processed in a laboratory and they usually take at least one day (and could take several days) to provide a result. PCR tests look for genetic material from the virus and can reproduce many copies of viral-related DNA from even the smallest sample.

What’s the fastest test for COVID-19?

Antigen tests are sometimes referred to as “rapid tests” or “at-home tests.” They can be processed almost anywhere, including in a doctor’s office, pharmacy, or even at home. They search for pieces of protein from the COVID-19 virus and can provide results in 10 to 15 minutes.

Antigen tests tend to be fairly accurate for people with symptoms but may not be as reliable if you have no symptoms. If you have symptoms and test positive with an antigen test, you most likely have COVID-19. You should isolate yourself and seek medical care as necessary. If you have symptoms and test negative, you should seek out a PCR test.

There are several FDA-authorized COVID-19 antigen tests that you can do at home and are available for purchase online or in a store. Visit the FDA’s website for a list of authorized self-tests. While antigen tests are very fast, they are less accurate than PCR tests.

Do all tests detect the Omicron variant?

No. The FDA has identified three COVID-19 tests that are not able to detect the Omicron variant. The agency issued a statement warning that at-home tests from Applied DNA Sciences, Meridian Bioscience, and Tide Laboratories will return false negative results.

Will the authorized tests tell me whether I have the Omicron variant?

No. In most cases, you won’t know which variant of COVID-19 you have, and your lab test typically won’t tell you. 


January 11, 2021


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