COVID-19 testing: When to test, how accurate are home tests and more

Now that COVID-19 is regularly circulating through communities, it’s hard to know if you should take a COVID test every time you have a sniffle. Gone are the days of COVID testing centers on every corner. But at-home tests remain readily available. When there’s an uptick in cases, you might be wondering when to get tested and the best kind of test to use.

As an infectious diseases expert and a hospital epidemiologist, here's what you should know about when to get a COVID-19 test, what kind you should use, what to do if you can't access one and why it's still important to get vaccinated.

When should I get a COVID-19 test?

It’s still a good idea to isolate and get a COVID-19 test if you have any cold symptoms, even if they’re mild and even if you’re fully vaccinated. Symptoms may include sniffles, congestion or a cough. COVID might resemble a mild cold, especially in fully vaccinated people. Know that even if you have minor symptoms, you are still contagious. People who are unvaccinated or immunocompromised may still get severe disease. Individuals with minor symptoms can go on to have complications related to COVID-19, so it’s important to know if you have the virus.

Rapid antigen tests vs. PCR tests: Is one better than another?

Rapid antigen tests – which you can buy in most pharmacies, big box stores and online retailers, are an excellent choice – but you may need to take multiple tests. 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 doesn’t necessarily mean you don’t have COVID-19. Trust a positive antigen test, but be more skeptical about a negative one. If you have symptoms of COVID-19 and your rapid test is negative, you should repeat the test according to the manufacturer’s instructions (usually 48 hours after the first test) or find a PCR test, which is more sensitive and usually done in-person at a doctor’s office or pharmacy. While you’re waiting for your second test’s results, you should keep wearing your mask and avoid contact with other people.

PCR tests are far more sensitive than antigen tests and can pick up COVID-19 earlier and stay positive for longer. While they’re considered the gold standard for a COVID-19 diagnosis, PCR tests are unnecessary for those who have already tested positive on an antigen test.

Where can I get tested?

There are still some free testing sites available. In Chicago, use this primary care doctor.

Home antigen tests are available at most pharmacies and big-box stores as well as online retailers. From time to time, the government also offers free tests you can order through the U.S. mail.

Regardless of where you get them, consider storing a few extras at home for when you need one.

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 don’t need to get another test to confirm the results. But if you have symptoms and you test negative, don’t rule out COVID-19 just yet. In this case, get a more sensitive PCR test or repeat your home antigen test according to the manufacturer’s instructions (usually 48 hours after the first test). While you’re waiting for your second test’s results, you should keep wearing your mask and avoid contact with other people.

If you’ve been exposed but don’t have symptoms:

If you are exposed but don’t have COVID-19 symptoms, using these tests before gathering with someone unvaccinated or immunocompromised will reduce (but not eliminate) the risk of spreading COVID-19. If you have any symptoms after being exposed to someone with COVID-19, you should assume you have been infected. Wear a mask around others and avoid contact with any immunocompromised or unvaccinated individuals.

Can I use an expired at-home COVID test?

Researchers continue to test the stability of at-home COVID-19 tests. Yours may be still valid after the expiration date. Check here to see if the date has been extended. The FDA does not recommend relying on any home test after the updated authorized expiration date.

How do I interpret at-home tests?

If you’re taking an at-home COVID-19 test, consider any positive result to mean you have COVID-19. You don’t need to confirm with a PCR test. (Even if it’s a faint line on the test strip, you should consider yourself infected and isolate.)

If you’re unclear about your test result, isolate and repeat the test in six to 12 hours. You’ll likely see a more apparent line on the test strip next time.

Don’t forget: a negative at-home test needs to be followed up with another test (either a PCR test right away or another at-home antigen test in about 48 hours).

I received an updated or annual vaccine. Why did I still get COVID-19?

While it’s still possible to contract COVID-19 even while vaccinated, your symptoms are more likely to be mild. The vaccine reduces the chance of severe illness, hospitalization and death. Like the flu, COVID-19 is constantly mutating, so getting the updated version of the vaccine provides the best protection for any new variants.

Plus, your immunity may have waned if you haven’t received that updated vaccine in a while. This is why everyone should get a new vaccine dose each fall. Immunocompromised people may be eligible for additional doses in between their annual vaccinations.

If you have any preexisting medical conditions, are over the age of 65 or are immunocompromised, you should contact your doctor right away to get prescription antiviral medication if you have COVID-19. This is important, even if you’ve received the most recent vaccination.

How long am I contagious if I have COVID?

According to the CDC, COVID-19 is most contagious in the first five days after the start of symptoms. You’re likely no longer contagious 10 days after the onset of symptoms. Experts like me, and the CDC, all insist that you wear a mask around others for at least 10 days from the time you develop symptoms.

Do updated COVID-19 shots offer added protection against new variants?

Like the flu shot, updated COVID-19 shots offer the best protection from new variants each season. Existing data show people who have received updated vaccines are the most protected Read more about updated shots here: What to know about updated COVID shots.