Can COVID Tests Detect New Variants?

Overhead view of person carrying out a Covid-19 rapid lateral flow test at home. She is holding a positive Coronavirus rapid self test device, feeling worried - stock photo

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Key takeaways

  • At-home antigen tests can still detect new variants, experts say.
  • Right now, the N protein—the part of the virus rapid tests detect—hasn’t changed enough to make antigen tests ineffective tools.
  • In order to get the most accurate test results, experts say to test repeatedly and a few days in a row.

New COVID variants like BQ.1.1 and XBB are circulating, causing concern that at-home rapid tests may not be effective at detecting them. But experts say that currently, our existing antigen tests can spot an infection—so long as you test properly and repeatedly.

Nathaniel Hafer, PhD, an assistant professor of molecular medicine at UMass Chan Medical School, said the variants we are now seeing may behave differently, but the part of the virus that antigen tests detect hasn’t changed. 

“The important thing to recognize there is that many of the mutations are in the spike protein. That's obviously important for immune evasion and how our body can recognize and fight off the virus,” Hafer told Verywell.

“But for rapid tests, many of them are designed to detect the N protein and that has not been mutating nearly as much, if at all,” he added. “We don’t have any reason to think that our tests would not be able to detect SARS-CoV-2.”

In fact, a new study published in science journal Cell found that rapid antigen tests efficiently detect all current and previous SARS-CoV-2 variants.

“Based on our findings, none of the major past and present SARS-CoV-2 variants of concern contain mutations that would affect the capability of current rapid antigen tests to detect antibodies,” study author Filipp Frank, PhD, an assistant professor in the department of biochemistry at Emory University, said in a statement.

How At-Home Rapid Tests Work and What They Detect

As Hafer said, rapid tests detect part of the virus called the nucleocapsid protein, or N protein. While the spike protein of the SARS-CoV-2 virus has indeed mutated since the start of the pandemic, the N protein in new variants is still detectable on antigen tests.

With rapid antigen tests, people either swab their nostrils or the back of their throat to collect a sample. That sample is then mixed in a tube with a liquid, then the mixed liquid is squeezed onto a test strip.

Antigen test strips have antibodies on them, which are just like the antibodies we have in our bodies that recognize foreign compounds. If you are positive for SARS-CoV-2, the swab sample will react with the antibodies on the test and show a positive result.

At-home antigen tests are accurate about 80% of the time in people who are infected with SARS-CoV-2. PCR tests have an accuracy rate of about 95%.

Rapid tests are proven to be effective at detecting Omicron—and BQ.1.1 is a new Omicron subvariant. Likewise, XBB is also descended from Omicron. That being said, there are some considerations when relying on antigen tests to detect these new variants.

What Might Affect How Well Rapid Tests Can Detect New Variants?

New variants are good at evading immunity from both vaccines and previous COVID infections, and may take a few days to show up on a rapid test due to the nature of their behavior: Omicron variants are known to be highly transmissible and can jump from person to person before they show symptoms, and can also be present in different parts of the body.

Colin Furness, PhD, an epidemiologist and assistant professor at the Dalla Lana School of Public Health at the University of Toronto, told Verywell that emerging variants may have different tissue tropisms—tissues where they prefer to replicate.

Furness explained that before Omicron, COVID was easily detected by swabbing the nose. Omicron evolved to prefer the back of the throat, which can affect test sensitivity—especially if you’re using a rapid test that relies on nasal samples.

To help with this, taking more than one rapid test improves accuracy and is more likely to yield a reliable result. This is because tests are most accurate when someone is at the highest peak of virus replication—which usually happens when they have symptoms.

Taking two to three tests a day apart from each other is ideal, as research has found that serial testing increases the accuracy of antigen tests.

Furness also said that we should be concerned about our current rapid tests if viral load—how much virus is being produced—should decrease with new variants. If that happens, it could be a problem for at-home tests. 

“Another issue is syncytia—the ability of a virus to cause an infected cell to fuse directly with another cell rather than bursting and sending out free virions,” Furness said. “This is done to evade the immune system and it could also make tests less sensitive.”

The research out of Emory University published in Cell didn’t just look at current variants; it also measured how mutations in the N protein could affect at-home tests’ accuracy and ability to recognize the virus.

Using a method called “deep mutational scanning,” the research team looked at possible mutations in the N protein. They then measured the impact of these mutations on their interaction with antibodies used in 11 rapid antigen tests and identified mutations that may allow for antibody escape.

Their findings concluded that while it’s pretty rare for variants to have N protein mutations that would evade detection on antigen tests, there are a small proportion of sequences that could. The authors wrote that this means public health officials and test makers should use data to determine if a rapid test needs to be tweaked for new variants in the future.

But for now, Hafer said we’re able to rely on the current rapid tests we have.

“We’ve seen in other viruses and in other tests, like rapid tests for flu, that they do need to be tweaked from time to time when the target has mutated to a certain degree,” he said. “We would imagine that at some point, the same kind of thing would need to be done for the SARS-CoV-2 virus. But we’re not there yet.”

What This Means For You

Rapid, at-home antigen tests can still detect new variants—including BQ. 1.1. and XBB. While we might need to tweak our antigen tests in the future, we are OK with existing ones for now. Experts say testing repeatedly for a few days will give you the most accurate results.

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.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Frank F, Keen MM, Rao A, et al. Deep mutational scanning identifies SARS-CoV-2 Nucleocapsid escape mutations of currently available rapid antigen tests. Cell. 2022;185(19):3603-3616.e13, doi:10.1016/j.cell.2022.08.010

  2. Emory University. Emory study predicts whether rapid tests will be able to detect future SARS-CoV-2 variants.

  3. Food and Drug Administration. At-home COVID-19 antigen tests-take steps to reduce your risk of false negative: FDA safety communication.

  4. World Health Organization. TAG-VE statement on Omicron sublineages BQ.1 and XBB.

  5. Smith RL, Gibson LL, Martinez PP, et al. Longitudinal assessment of diagnostic test performance over the course of acute SARS-CoV-2 infection. J Infect Dis. 2021;224(6):976-982. doi:10.1093/infdis/jiab337

By Laura Hensley
Laura Hensley is an award-winning lifestyle journalist who has worked in some of the largest newsrooms in Canada.