Millions of coronavirus tests that can deliver results in 15 minutes will be available in September, but they're less accurate

• Millions of rapid coronavirus tests are slated to become available to people across the US next month.

• The tests, which can yield results in around 15 minutes, are cheap and easy to produce, and require no lab work.

• But they are generally not as accurate as laboratory PCR tests, and may need to be performed several times to get an accurate read on whether someone is actually sick.

• "I would still say that distancing and outdoor air are your best friends," one expert said.

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US coronavirus testing is about to get a whole lot speedier.

After months of testing shortages and delays using laboratory tests, the US is beginning to embrace a new kind of diagnostic coronavirus check: the point-of-care test, which can yield results in around 15 minutes, with no trip to a lab.

"We're not in a situation where every American can wake up in the morning and have a test that they get before they go to work, but there are plenty of tests, and that's growing substantially," Admiral Brett Giroir, the US coronavirus testing czar, said on a call with reporters on Wednesday.

The trade-off in this quest for faster tests, and more tests available on-site at places like nursing homes, schools, and businesses, is accuracy.

"I would still say that distancing and outdoor air are your best friends, keep that in mind," Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota, told Insider.

That's because these newer, rapid tests are not as foolproof as the laboratory kinds of checks that have been in use for COVID-19, the disease caused by the novel coronavirus, for months now.

(Just ask Ohio Governor Mike DeWine, who recently had a rare false positive rapid test before he was slated to meet President Trump, an experience that led him to emphasize that quick tests should be "looked at as a screening," and not definitive coronavirus diagnosis tools.)

The US is planning to have 40 million rapid tests available next month, a dramatic uptick

Coronavirus test results in the US have typically taken multiple days to return, a delay that helps propel the virus's spread.

"The majority of the testing is absolutely useless, because the results don't come back in 24 hours," Bill Gates recently told Insider.

With the virus still taking hold in many pockets of the country, rapid tests — though imperfect — are on track to become the country's next big tool in better fighting the pandemic.

"In September, we should have upwards of approximately 90 million, nine-zero-million tests available," Giroir said. "Probably about 40 million of that will be point-of-care."

If his monthly forecast holds true, it would be a remarkable uptick in US testing, more than doubling the number of tests the country has performed to date (74.8 million so far, according to Giroir).

These tests are intended for people in essential services and vulnerable populations, not the general public

Giroir argues that the tests could be especially useful in places with major outbreaks, like nursing homes and schools.

"Random testing of healthy people, just all over the country, is not what we're advocating for," he said. "Point-of-care tests are extremely useful if you have symptomatic people, or if you're contact tracing, or if you're in a place like a nursing home where we're going to be testing repeatedly."

Giroir called this quick brand of antigen testing an "old school" viral technique that's useful because it is cheap, and production can happen fast. (Antigen testing has been used before to detect influenza and other respiratory viruses.)

"You can lose a little sensitivity, which generally these tests do, because you're going to have repeat testing," he said. "A little bit of loss of sensitivity, particularly in a nursing home, if you can get a rapid turnaround, beats a very highly sensitive test at a two- or three-day turnaround."

But many people are already using rapid test results in more dangerous ways, as a kind of permission slip to live life and party as if the coronavirus didn't exist.

"The question is, at what point do you feel comfortable if you're going to put yourself or others at risk of infection?" Osterholm said. "These tests can sometimes be a deterrence to exercising good judgment."

How rapid tests work

Most rapid tests work by hunting for the presence of coronavirus antigens in fluid samples collected from a sick person's nose or throat. Antigen tests scan for bits of protein that sit on or in the coronavirus, instead of doing a more in-depth scouring for the virus's genetic code, like molecular lab tests (RT-PCR) do.

Because there are so few of the rapid antigen tests approved for use in the US (just three have been granted emergency authorization by the US Food and Drug Administration thus far), it's tough to know exactly how well they perform. Osterholm estimates the tests may pick up on somewhere around 7 to 8 in every 10 coronavirus infections, leaving 20 to 30% of coronavirus patients in the dark about their status, and blissfully thinking they're virus-free. (A false positive test result, like DeWine's, is rarer than a false negative.)

"Rapid antigen tests are particularly helpful if the person is tested in the early stages of infection" the US Centers for Disease Control and Prevention said in guidance about the rapid tests released last week, emphasizing they work best on people with a high viral load (usually, a person's viral load is highest in their first day or two of infection).

Rapid tests should not be used as a permission slip to be reckless

Cheap rapid tests have already been dispatched in other places around the world to track the virus, including in free-of-charge government testing on the streets of New Delhi, India, and among sports teams and vacationers in the UK and Poland.

But even if rapid coronavirus test results are accurate more often than not, they are not a free passport to carefree living right now. Being in close proximity to other people and their germs is still a risky prospect.

"A negative test one day does not mean you're going to be negative the next day," Giroir said.

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