With COVID cases on the rise, it might be time to break out the rapid tests before (or after) a big gathering, or when you have a cough.
Though BA.5 is great at sneaking past vaccines and even immunity from prior infections, researchers say that rapid tests can probably still detect BA.5—after all, they’ve worked on all the other variants. But aside from the usual caveat to take a negative test with a grain of salt, there are some snags in rapid testing to be aware of as the pandemic wears on.
Rapid tests work like this: if the virus is present in your carefully-swabbed sample, certain compounds in the rapid test will recognize it, bind to the virus, and elicit a tell-tale second line. Typically rapid tests target a part of the virus called the nucleocapsid, a protein that envelopes the RNA of the virus, and doesn’t change much between variants. “Because of that, the tests are able to detect the different variants,” says Nate Hafer, an assistant professor of molecular medicine at UMass Chan Medical School. Nucleocapsid proteins are super abundant in the virus, making them an effective target for tests.
The part of the virus that does mutate from variant to variant is the spike protein. “The spike protein is important from an immunological and vaccine performance perspective, Chana Davis, who is on the rapid test beat at at Dear Pandemic, said. “But when you’re talking about rapid test performance, the spike protein is irrelevant.”
That being said, you still might be hearing accounts of people’s tests not “working as well” as they have before. It’s true that rapid antigen tests are generally not as good as they were in the pre-omicron days at detecting COVID right when symptoms appear.
This difference has to do with the progression of the virus. Each variant has different “tissue tropisms,” meaning that they enter different parts of the body at different points in the infection. With later variants, you might feel the virus in some parts of your body before you have enough of it in your nose to show up on a test. So while rapid tests probably do work with new variants, the fact that these variants present differently throughout the body can influence how many lines initially show up on your test.
But Davis noted that the timing of symptoms and levels of virus just varies from person to person, and there are people who test positive on the first day of symptoms. She recommends not putting too much faith into a single result in general, as it’s only a snapshot in time.
And how do you get the most accurate snapshot? Repeat sampling.
“We did a large study in collaboration with the FDA and the results of that study are going to be published pretty soon showing the value of the serial testing,” Hafer said. “With an antigen test, they really are designed to be two tests, one after the other, or maybe three tests, to really be able to capture that period where the virus is incubating in the body and building up. Our study shows that two or three tests taken together can have the same accuracy as a PCR test.”
There’s one more thing to look out for: if you still have any of the tests the government sent out in January, you should probably check the authorized expiration date on the packaging (though some have been extended by the FDA). And if you’re looking for more tests, the government announced on Monday that they are sending out eight more tests per household—an improvement on the previous shipments of four at a time. Happy swabbing!