Regular COVID-19 testing is one of the best ways to minimize virus transmission, and rapid at-home tests make it more convenient to do. However, the continued mutation of the virus has brought rapid antigen tests’ diagnostic performance into question.

Key Takeaways

  • New research suggests that some rapid antigen tests are not sensitive enough to detect asymptomatic COVID-19 infections.A person’s viral load, respiratory secretions, and the window of infectiousness for the virus may affect the ability of a rapid antigen test to detect Omicron.People who test negative with a rapid COVID test should test again after 48 hours.

“Rapid antigen tests remain effective public health tools in detecting COVID-19 caused by Omicron,” Bobby Brooke Herrera, PhD, an assistant professor of global health at the Rutgers Global Health Institute, told Verywell. “For the most part, they are not impacted by the Omicron mutations in terms of detecting high virus load.”

Based on early data from the Food and Drug Administration (FDA) and the National Institutes of Health’s (NIH) RADx program, rapid antigen tests do detect the Omicron variant—but the sensitivity might be lower. Here’s what that means for asymptomatic infections.

Can Rapid Tests Detect Asymptomatic COVID?

Marc Sala, MD, co-director of the Northwestern Medicine Comprehensive COVID-19 Center, told Verywell that while Omicron does show up on rapid antigen tests, new data suggests that there may be more false negatives in people who are asymptomatic.

A recent study published in Clinical Microbiology and Infection looked at the diagnostic accuracy of three common rapid antigen tests—Flowflex, MPBio, and Clinitest—using positive RT-PCR tests as the standard.

Bobby Brooke Herrera, PhD

Rapid antigen tests remain effective public health tools in detecting COVID-19 caused by Omicron.

The researchers found that the sensitivities of the tests were very low for asymptomatic people who did unsupervised nasal self-sampling during the Omicron period. The sensitivity of the tests ranged from 20.7% to 27.5%. 

“This is likely a problem of the viral load being too low for the test to pick up consistently, as well as asymptomatic persons having fewer respiratory secretions to generate a good sample,” Sala said.

What Is Sensitivity?

Sensitivity is the percentage of people who are infected who actually show a positive test result.

Does Self-Testing Still Matter?

The authors of the study pointed out that self-testing could lead to a false sense of security among asymptomatic people who want to protect vulnerable people. That’s why it’s still important to practice social distancing and wear face masks. 

“I would add that not all home test kits are created equal—nor are all operators,” said Sala. “Studies with trained healthcare providers doing numerous numbers of these tests every day versus studies where patients conduct the test at home may not have the same results for test sensitivity.”

According to Herrera, it’s possible that the rapid antigen tests just missed Omicron’s window of infectiousness. If that’s the case, it’s not that tests cannot detect Omicron—rather, it could be that swab sampling for the virus might not be adequate enough to fully detect people with asymptomatic infections.

The study authors noted that a throat swab in addition to a nasal swab might increase the sensitivity of the antigen tests, but they are still unlikely to reach acceptable levels.

In any case, self-testing for COVID regardless of symptoms is still useful because any identified infection helps reduce transmission and prevent exposure to other people.

When Should You Take a COVID Test?

You should always get tested after having close exposure to someone with a known COVID infection to monitor yourself for symptoms. That said, do not test immediately—especially if you do not have symptoms. Otherwise, you might get a false negative.

“If someone was exposed to SARS-CoV-2 and does not have symptoms, they should wait at least five full days after exposure before testing with an antigen test or by PCR,” Herrera said. “Testing too early can often lead to an inaccurate result.”

If someone was exposed to SARS-CoV-2 and does not have symptoms, they should wait at least five full days after exposure before testing with an antigen test or by PCR.

COVID testing should not be limited to people with recent exposure to the virus or people who currently have symptoms—it should also take place before entering any healthcare setting or gathering with people who are immunocompromised.

“For an asymptomatic person, COVID-19 testing is used prior to exposure to groups particularly vulnerable to infection, including people unable to mount adequate immunity to vaccines,” Sala said.

Asymptomatic infections might be harder for some tests to detect, which only reaffirms the importance of repeat testing. Should you test negative, Sala and Herrera recommend testing again 48 hours later to improve the diagnostic yield and ensure that a COVID infection is not missed.

“As mutations become more frequent in the spike and nucleocapsid sequences of the virus with future variants, the rapid antigen test technology may need to be updated,” Sala said. “However, a positive test remains nearly 100% diagnostic for Omicron, so a positive test should not be ignored.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

What This Means For You

Rapid antigen tests do detect the Omicron variant and are still important public health tools in minimizing the spread of COVID-19. However, new research suggests that asymptomatic people might not have enough viral load to test positive with a rapid test, so repeat testing is highly recommended.