Think you have COVID? New research suggests you should wait to test for it.

As COVID cases climb across the country , a new study from the University of Colorado Boulder suggests you shouldn't test for the virus as soon as you start feeling sick.

What they found: In a paper published this month in the journal Science Advances , researchers found it's best to wait two days after symptoms arise to take a rapid test, since the virus is likely undetectable until then.

• That's because most people's immune systems now react quickly due to prior exposure, but new variants in people with some immunity develop slower than the original strain.

By the numbers: Patients with Omicron variants received a false negative as much as 92% of the time when they tested immediately, but that figure dropped to 70% when they waited 48 hours.

• Taking a second test on the third day lowers the false negative rate even further, to 66%, researchers found.

Yes, but: For flu and RSV, it's best to take a rapid test as soon as symptoms show up, first author Casey Middleton said in a statement.

• Flu and RSV viruses multiply rapidly when symptoms first start, so there's plenty to make a test show up positive from the get-go.

What they're saying: "This is the conundrum," according to senior author Daniel Larremore.

• "If you go in right away and test for all three, you can learn a lot from the flu and RSV tests, but you may have swung too early for COVID. If you wait a few days, the timing might be right to catch COVID but you are too late for flu and RSV."

State of play: Colorado's COVID rate remains low, but cases have been ticking up over the past several weeks, state health officials say.

• "We have seen a shift away from JN.1 to newer KP1.1, KP.2, KP.3, and other strains," Kayla Glad, a spokesperson with Colorado's health department, tells us.
• "Those could be causing some of these increases, in addition to other factors such as summer travel and spending time indoors with air conditioning," she says.

The bottom line: If you do test positive for COVID, CU Boulder researchers recommend a "test to exit" strategy, in which you test until you receive a negative result, instead of following the CDC's previous "five-day isolation policy," which it abandoned in March .

• "The five-day isolation policy made people isolate for too long in most cases," said Middleton. "Test-to-exit does a good job releasing people early who aren't going to transmit but holding those who still have high amounts of virus."
• State health officials recommend testing twice, 48 hours apart if you do have symptoms or three times, each 48 hours apart, if you aren't showing signs.