As the COVID-19 pandemic enters its fourth year, a negative result on a little plastic at-home test feels a bit less comforting than it once did.
Still, you dutifully swab your nostrils before dinner parties, wait 15 minutes for the all-clear and then text the host "negative!" before leaving your KN95 mask at home.
It feels like the right thing to do, right?
The virus has mutated and then mutated again, with the tests offering at least some sense of control as the Greek letters pile up. But some experts caution against putting too much faith in a negative result.
So it's only fitting to do a reality check on what those rapid COVID-19 tests, also called antigen tests, can do — and what they can't.
Is the latest omicron variant tripping up at-home tests?
For the most part, the answer is no.
That's because as the virus evolves, scientists are mainly seeing changes in its spike protein, which is what the virus uses to attack and enter healthy cells. But the rapid antigen tests aren't actually looking for that spike protein.
"[The tests] rely on detection of the nucleocapsid protein, which is the protein that is directly encapsulating the viral RNA," says Dr. Robin Colgrove, a professor at Harvard Medical School and chair of the Diagnostics Committee of the Infectious Diseases Society of America.
He says this interior protein really hasn't changed much as the virus has mutated over the years. So, at least for now, the rapid tests can detect it.
Federal health agencies are monitoring the situation in case that changes. The Food and Drug Administration is working with the National Institutes of Health to study just how well the at-home tests work as the virus continues to evolve.
So far, the agencies have identified only one test — the Luminostics Inc. Clip COVID Rapid Antigen Test — that has been rendered less reliable in the face of new variants. And even then, the FDA says "the impact does not appear to be significant."
Are antigen tests taking longer to show a positive?
Some people report having negative antigen test results for days, despite having a known COVID-19 exposure and the telltale symptoms. Eventually, they test positive, but it can sometimes take as long as a week.
The phenomenon is somewhat mysterious, says Colgrove. He acknowledges that doctors are seeing it, but so far, it's only anecdotal.
"What kind of an experiment would you have to do to answer that question?" he says, explaining that it would be difficult to study.