When Should You Test (and Possibly Retest) After Being Exposed to COVID?

Most of us have likely been exposed to the COVID-19 virus multiple times. If you've been in close contact with someone who has COVID—or who later tests positive for COVID, it's recommended to test yourself for the virus at around day five after exposure or the first sign of symptoms.

It's important to wait to test, as it can take several days for your body to build up enough antibodies to test positive. You can spread COVID even if you don't have symptoms. While the Centers for Disease Control and Prevention (CDC) no longer has strict guidelines for isolation and masking after exposure, the CDC recommends testing to prevent the spread of infection and expedite treatment for those at high risk of complications.

When Should You Test for COVID?

The general rules behind testing for COVID have remained mostly the same throughout the pandemic. However, due to the way that newer variants behave in our bodies, there are a few things to be aware of while you're testing.

You've been exposed to COVID if you've been in close contact with someone with the infection, whether they are showing symptoms or not.

"To meet the definition of 'close contact' you generally need to have spent at least 15 minutes of time in close proximity while the other person was ill or in the two days prior to them becoming ill," Sujit Suchindran, MD assistant professor in the division of infectious diseases at the Emory University School of Medicine, told Health.

The best time to test—and to ensure that you're going to get an accurate result—is around five days after you've been exposed to the virus, or when you first start experiencing symptoms. The day of exposure is considered day zero.

"If you're incubating the virus, you may have a false negative test if you test too early," said Dr. Suchindran. "If you haven't developed symptoms, testing around day five after exposure is ideal."

COVID Exposure Timeline

The average incubation period for pre-Omicron variants is 5 days but ranges from two to 14 days after exposure. The Omicron variant seems to be up to three times more transmissible, but it has a shorter average incubation period—typically about two to three days. Newer variants may have shorter or longer incubation periods but the rule of thumb is to test at day five or the onset of symptoms, whichever is sooner.

Your incubation period may also vary based on age. One 2022 study found a relatively short period of Delta and Omicron variant infection in young, healthy adults who were previously vaccinated. The average length of time for testing positive was two to three days, and only 17% of participants tested positive five days after the onset of symptoms.

Delayed Positive Testing

COVID symptoms can start to show anywhere from two to 14 days after exposure. However, that doesn't always mean you'll get a positive result on your test right away even if you have contracted the virus.

"We're seeing a lot of delayed positivity with testing," Amy Karger, MD, PhD, associate professor at the University of Minnesota Medical School, told Health. "People are having symptoms for one to three days with negative tests, and then they'll turn positive after a few days with the COVID testing. And that was not happening with prior variants."

The delayed positivity makes it more difficult to trust a negative test result, especially in the first few days.

It's unclear why the delayed positive test results are happening, but researchers have some theories. Dr. Karger said that one guess is that the Omicron subvariants may replicate more in the throat, so there may not be enough virus for nasal swab COVID tests to detect early on.

Another possibility, Dr. Karger added, is that because most people have some level of immunity from a prior infection or a vaccine, those early symptoms may just be our immune system doing its best to fight off the virus.

Do I Need To Quarantine After Exposure?

You might not develop COVID until 10 days after exposure and you can pass on the virus before you get symptoms. However, as of 2024, you are no longer required to isolate after exposure to COVID. Still, it is recommended to mask, keep social distance, and use other precautions if you may have the virus. These steps are particularly important if you show any COVID symptoms or are around anyone at higher risk of infection, such as people who are unvaccinated, older, or immunocompromised.

If Your Test Was Negative

If you were exposed to COVID, a negative at-home (antigen) test doesn't mean you don't have the infection. If you get a negative test but want to be sure that you are not infected, follow this testing protocol:

• Take preventative measures (e.g., wear a mask) to protect others
  
• Watch for symptoms
• Test again 48 hours later or if you have symptoms
• If negative again, wait 48 hours more and test again

You could also get a PCR laboratory test instead of doing repeat at-home testing. Though the turnaround time is a bit slower, PCR tests are more sensitive and may be able to catch the virus in those earlier stages. Self-tests are often better at detecting COVID if you already have symptoms.

A Quick Review

General recommendations are to test five days after potential exposure to COVID if you are asymptomatic. Test right away if you notice symptoms. However, a negative test does not necessarily mean you don't have COVID or won't develop the infection, especially if you use an at-home antigen test. You also might not test positive until several days after symptoms begin.

Use the CDC and FDA websites as guides for the most recent information regarding when and how to test for COVID, as they continue to shift based on new variants. Contact a medical provider for further guidance and to address any questions you have about testing for COVID.