When should I use a rapid COVID test, and how accurate are they? – UChicago News

As the very infectious Omicron variant of COVID-19 surges around the country, you need to know what kind of tests to take to protect yourself and your community.

Emily Landon, infectious disease expert and executive medical director for infection prevention and control at University of Chicago Medicine, answers common questions about COVID-19 tests.

These include when to get a COVID-19 test, what kind you should use, what to do if you cant get one at all, and why its still important to get vaccinated and boosted.

Q: When should I get a COVID-19 test?

Isolate and get a COVID-19 test if you have any symptoms of COVID-19, even if theyre mild and even if youre fully vaccinated and/or boosted. Symptoms may include sniffles, congestion or a cough, and might resemble a mild cold, especially in fully vaccinated and boosted people.

Even if you have minor symptoms, you are still contagious. People who are unvaccinated or immunocompromised may still get severe disease. Stay isolated if you have any symptoms, even if you cannot quickly get a COVID-19 test.

Q: How are rapid antigen tests different from PCR tests? Is one better than another?

Rapid antigen tests, which you can buy in most pharmacies, are great in specific circumstances and less good in others. Rapid antigen tests detect COVID-19 when people have a higher amount of virus particles in their system and are more contagious. But a negative antigen test doesnt necessarily mean you arent contagious. If someone has COVID-19, but hasnt yet reached the tests threshold of viral particles, they may still test negative with an antigen test but positive on a PCR test. Thats why I tell people they should trust a positive antigen test, but be more skeptical about a negative one.

PCR tests, which are still mostly done at hospitals and other testing facilities rather than at home, are far more sensitive than antigen tests. Theyre able to detect smaller quantities of the virus and detect them sooner (and for more time) than antigen tests.

While theyre considered the gold standard for a COVID-19 diagnosis, PCR tests are unnecessary for those who have already tested positive on an antigen test. Thats important to know as wait times for PCR tests grow due to increased demand.

In short: any positive test counts as a positive, but a negative antigen test needs to be confirmed with a PCR test.

Q: When should I use an at-home test?

A rapid, at-home antigen test is a useful tool to have in your COVID-19 arsenal. But you need to know when and how to use these tests.

If you have symptoms:

If you have COVID-19 symptoms and test positive on an at-home test, you have COVID-19. You dont need to get another test to confirm the results.

But if you have symptoms and you test negative, you should not rule out COVID-19 just yet. In this case, we recommend getting a more sensitive PCR test. If you cant get in for a PCR test quickly, its recommended to repeat the antigen test the following day, being sure to isolate until you get your PCR test and results. If you cant get a PCR test at all, isolate for 10 days.

If you dont have symptoms:

For those without COVID-19 symptoms, using these tests before a gathering will reduce (but not eliminate) the risk that someone attending has COVID-19. Remember: antigen test results can change quickly, and a negative result is really only trustworthy for eight to 12 hours.

In other words, you shouldnt rely on a negative test in the morning if you want to get together in the evening with friends or family. Make sure everyone whos attending an event uses an at-home test as close as possible to the time theyre gathering and understands that a negative test doesnt guarantee safety or completely prevent exposure.

If youve had a known COVID-19 exposure, no test is going to make it safe for you to gather unmasked with high-risk individuals. Stay home.

Q: How do I interpret at-home tests?

If youre taking an at-home COVID-19 test, consider any positive result to mean you have COVID-19. You dont need to confirm with a PCR test. (Even if its an extremely faint line, you should consider yourself infected and isolate.) If youre unclear about what your test result says, isolate and repeat the test in six to 12 hours. Youll likely see a clearer line on the test strip next time.

Dont forget: a negative at-home test is only reliable for eight to 12 hours and still doesnt guarantee youre COVID-free. You should get a PCR test if you have symptoms.

Q: What should I do if I cant get a COVID-19 test?

Given the widespread transmission of the Omicron variant, if you have symptoms, you should assume you are infected with COVID-19, regardless of your vaccination status. Isolate for the amount of time thats recommended by the health department.

Q: What should I do if Ive been exposed?

If youve been exposed, but have no symptoms and you are fully vaccinated and boosted, you dont need to quarantine. But you should get a test on Day 4, 5, or 6 following your exposure. (For example, if you were exposed on Monday, you should get tested on Thursday, Friday or Saturday.) If you develop symptoms, assume youre infected and begin isolation.

If youve been exposed and are vaccinated but not boosted, you need to quarantine for five days after an exposure and wear masks for another five days after that. You are still at high risk of infection, especially from the quickly spreading Omicron variant. You should wear a mask around other people, and get tested four to six days after the exposure and anytime you develop symptoms. Avoid gatherings and do your best to limit contact with people who are immunocompromised or who are unvaccinated.

If youve been exposed, have no symptoms, but are NOT vaccinated, stay home and quarantine for five days. Youll need to wear a mask for another five days after that.

Q: Im vaccinated and boosted. Why did I still get COVID-19?

COVID-19 vaccines and boosters are hugely valuable. In addition to providing protection from the virus, vaccines and boosters reduce the chances of serious illness, hospitalization and death. But people can still get infected when theyre fully vaccinated and boosted. This may be because the vaccines protection has decreased over time or because a new variant (like the Omicron variant) is better at getting around the vaccines protective properties.

COVID-19 infections in fully vaccinated people are called breakthrough infections, which usually result in milder symptoms versus infections in the unvaccinated. Your bodys memory B cells and T cells, which developed after your vaccine, respond quickly to stop the infection and prevent severe damage. Immunocompromised people may not have strong B cell- and T cell-immunity even after vaccination, so they remain at higher risk. If you are immunocompromised and have a breakthrough infection, you should contact your doctor even if you only have mild symptoms.

Unvaccinated people dont have existing antibodies or memory B cells or T cells waiting to fight off COVID-19, so they have to start their immune response from scratch if they become infected. Infections typically cause more damage to their organs and tissues, which can lead to complications like having low oxygen levels, as well as problems with the lungs, kidney and heart. Unvaccinated individuals are also much more likely to need intensive care support or have lingering symptoms known as long COVID-19.

Q: If I have a breakthrough infection after my COVID-19 vaccine, will I still be contagious for the same amount of time?

Theres a good amount of evidence showing most fully vaccinated and boosted people with breakthrough infections are both less contagious, and contagious for a shorter time. Theyre also more likely to get mild infections.

Q: Can I report my positive at-home test results to public health officials?

At-home antigen test results are not typically reported to public health agencies, nor are they usually included in official case tallies. This means statistics are significantly under-reported. In some communities, local health departments are setting up portals for people to self-report at-home results, but youll need to check to see whats available in your area.

The most important thing to do is stay home and isolate. If you have certain health conditions especially if youre immunocompromised contact your doctor ASAP so they are aware of your diagnosis.

Q: When can I get the new medicine thats received emergency use authorization to fight or prevent COVID-19?

The good news is that new antiviral medication and a preventative monoclonal antibody treatment have received emergency use authorization from the U.S. Food & Drug Administration. Theyll be very important resources for doctors and high-risk patients. Even so, these treatments will be extremely limited at first. They will first be distributed by public health agencies and will only be available to the highest-risk patients.

If you are a transplant recipient, have a primary immunodeficiency, take immunosuppressive medication, or are undergoing active chemotherapy, and you test positive for COVID-19, you should contact your doctor right away to see if any of these treatments are available to you.

Q: Do COVID-19 booster shots offer added protection against the Omicron variant?

A: Boosters offer the best protection from catching Covid, but they arent perfect. Scientists are still gathering data on the effectiveness of vaccines against Omicron, but existing data show people who are vaccinated and boosted have additional protection and are less likely to be hospitalized than those who are unvaccinated. Read more about booster shots and third doses here: What to know about booster shots and third doses of the COVID-19 vaccine.

Adapted from an article published by UChicago Medicine.

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When should I use a rapid COVID test, and how accurate are they? - UChicago News