The Omicron BA.5 variant—the strain of COVID-19 that’s currently dominating in the United States—is good at evading immunity from both vaccines and previous COVID infection. There’s also concern that rapid at-home antigen tests are less effective at detecting the variant, too.
When Omicron first hit in late 2021, the FDA said that antigen tests do detect the variant but that the tests may have reduced sensitivity.
A diagnostic test’s sensitivity is a measure of how often it shows a positive result when a person really is sick.
If a COVID test has low sensitivity, it means there’s a higher chance it will give a negative result to people who are sick (false negative).
Researchers have been trying to figure out how well rapid tests spot an Omicron infection. They’ve concluded that while at-home COVID tests can pick up Omicron variants—including BA.5—there are some key steps that people need to take to get an accurate result.
Phyllis Kanki, DVM, DSc, a professor of health sciences at Harvard T.H. Chan School of Public Health, told Verywell that “studies conducted—including our own—showed that rapid antigen tests maintained their ability to effectively detect Omicron.”
Since BA.5 is part of the Omicron family, Kanki said it’s not been anticipated that at-home tests will be less effective.
Nathaniel Hafer, PhD, an assistant professor of molecular medicine at the University of Massachusetts Medical School, agreed with Kanki, adding that antigen tests can detect BA.5 because of how they are designed.
Hafer said that the test strip on rapid tests has antibodies on it, which are made in the lab. They’re just like the antibodies we have in our bodies that recognize foreign compounds—otherwise known as antigens.
“Those antibodies are designed to bind to parts of the virus,” said Hafer. “Typically, they are binding to what’s known as the nucleocapsid protein, which is one of the most common proteins that’s in the highest abundance in the virus.”
While the spike protein on the SARS-CoV-2 virus has mutated with Omicron variants, Hafer said that the nucleocapsid tends to mutate at a relatively low rate. In other words, the antigen tests can spot the nucleocapsid found in BA.5.
While experts say that at-home COVID rapid tests can detect BA.5, there are some key things to be aware of before you test if you want to ensure you get an accurate result.
For example, with the new variant, some people have reported having COVID symptoms and testing negative with a rapid test for a few days before getting a positive result. Others say that they’ve tested negative for two days in a row, only to become positive on day three.
Hafer said there are a few reasons why this could be happening. First, it can take a few days for the COVID virus to build up in the body.
“There can be a period early in the infection where the virus is present, but it’s not present at high enough levels to be detected on these kinds of tests,” said Hafer, adding that this is particularly true when somebody is first showing symptoms, or when they’ve just been exposed to somebody who is COVID positive.
PCR tests typically show a COVID infection one to two days before a rapid test does because they’re more sensitive.
Since BA.5 is highly transmissible and can jump from person to person before they show symptoms, it could be a few days before someone develops obvious symptoms and tests positive.
Another reason that Hafer cites has to do with where the COVID virus is in the body. The Omicron variants seem to be more in the throat than the nose, which could affect the sampling technique of antigen tests.
Research by the Ontario COVID-19 Science Advisory Table found that rapid antigen tests are less sensitive for the Omicron variant compared to the Delta variant when samples are taken from the nose—especially in the first couple of days after infection. Therefore, the researchers concluded that oral-nasal samples may detect Omicron more reliably.
For any strain of COVID, the key to getting a reliable result from a rapid at-home test is taking it the right way. According to Kanki, “the accuracy of the rapid tests requires that the instructions for the rapid tests be followed completely.”
Hafer adds that this means if a test’s package says to use a nasal swab, don’t take it upon yourself to swab in a different way.
Taking more than one rapid test also improves accuracy. Hafer said that many of the tests are designed to be used in sequence—for example, taking two tests 24 to 48 hours apart.
Research has shown that serial testing multiple times per week increases the accuracy of rapid tests. Hafer said that this is because “especially early on, there can be that period of virus increasing in the body.”
Once you’ve taken a test and gotten results, Hafer said to “wait another 24 to 48 hours before you do a second test.” According to Hafer, the results of those “two tests together have the combined accuracy, in many cases, of a PCR test.”
Kanki adds that at-home rapid tests are very good at detecting the virus during the highest peak of virus replication (usually when a person shows symptoms).
The bottom line? If you follow instructions and take two or more tests in sequence over the course of a few days, you can probably rely on the information you’re getting.
“The tests still detect Omicron,” said Hafer. “And so people should feel confident that they’re working, and that they can trust the results.”
At-home antigen tests can detect BA.5. However, to get accurate results, experts advise that you follow the test directions to the letter and take multiple rapid tests a few days apart.
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