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The Food and Drug Administration (FDA) is under fire for being too slow to approve at-home tests in the coronavirus crisis.

Earlier this month, the agency announced it would allow labs to sell tests, and apply for emergency approval 15 days later. Several companies jumped to offer their tests in a use-at-home format, and some even began selling them.

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Most of the tests were to be taken by an individual at home, and then would be mailed to an approved lab for analysis – a process already used for many medical tests.

But on March 20, the FDA updated their guidance, saying their regulatory waivers "do not apply to at-home testing, including self-collection of samples to be sent to a clinical laboratory."

That forced the companies offering at-home tests to immediately shut down sales.

Ten days later, no at-home kits have been approved by the FDA. The FDA defended its action and said it wants to ensure tests are accurate

“It is critical to ensure that home collection and transport of specimens to labs still provide for accurate test results,” an FDA spokesperson told Fox News by email.

But critics say the approach is too cautious.

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“It’s baffling,” Danielle Bradnan, a researcher and biologist at consulting firm Lux Research, told Fox News. “Everlywell was wrapping up the infrastructure to be able to handle [up] to a quarter-million of these tests a week and they were ready to launch last Monday."

Everlywell had 30,000 use-at-home kits ready to go before regulations put their sale on hold. The company instead directed those kits to hospitals. Their test kit, if approved, would sell for $135. Two other health testing companies – Carbon Health and Nurx– had already begun sales of at-home kits before having to halt them.

“We have stopped all new test requests,” Nurx’s website said.

The FDA said that it has concerns about at-home kits, because after the user takes a sample, it then gets shipped to labs, and the shipping could reduce reliability.

“Self-collection at home or at sites other than designated collection sites staffed by [health care providers] raise concerns regarding specimen stability, transport, and appropriate collection materials,” the FDA said in a statement to Fox News.

The FDA last week approved people to self-test under the guidance of health care workers at an approved location, after a study found that an easy-to-collect sample from the nostril is usable (previously, a sample had to be taken from behind the nasal cavity, which would have been extremely difficult to self-collect.)

Bradnan noted that the labs selling the kits already offer approved testing for sexually transmitted diseases in the same at-home way.

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“The companies’ whole infrastructure is based on this method. Apparently the FDA doesn't have a problem with them doing at-home testing for STDs,” Bradnan said.

“Unless there's something huge that they're not disclosing, I don't understand why it's not okay for the tests to be done at home, and mailed in,” she added.

The FDA said that the hold up is worth ensuring the accuracy of the test.

“False results can lead to significant adverse public health consequences, especially during an unprecedented public health emergency,” it added.

The FDA said it is “actively working with test developers in this space,” and a spokeswoman for Everlywell said the company is working with the FDA to get approval.

“We have been meeting regularly with the FDA since they made their statement last Friday to discuss a path forward for an at-home sample collection test,” Christina Song, director of communications at Everlywell, told Fox News.

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“The test will likely use a short nasal swab for easy collection and will include free telehealth consultations with an independent physician for those with positive results to receive diagnosis at home. We hope to make it available to the public soon,”

The FDA said it is evaluating applications for at-home test kits but did not provide a timeframe for the first approval. An FDA spokeswoman said that once a full, detailed application with data is received, it can sometimes be approved as quickly as within 24 hours.

“The FDA is interested in early interactions with test developers and we encourage them to reach out to us to begin pre-EUA discussions, even if they do not have validation and/or documentation completed,” the agency said in a statement.

Asked what kind of data test creators needed to submit, an FDA spokesman pointed to section V of FDA guidelines requiring a minimum of 60 experimental tests, among other things.

Economists who study regulation argue the FDA is being too strict.

“Right now, we need as many tests as possible and it doesn't make sense to overburden nurses, hospitals and clinics with potentially sick people. The FDA has repeatedly delayed new tests, putting the United States weeks behind at the expense of lives,” Alex Tabarrok, an economics professor at George Mason University, told Fox News.

Many experts believe that the path out of the pandemic involves widespread testing of nearly everyone; then infected individuals can be identified and quarantined, while the rest of the country can go about their lives and revive the economy.

Data from Iceland, and the Diamond Princess cruise ship, show that nearly half of people with the coronavirus do not show symptoms, but can still spread the disease. Very widespread testing would be needed to identify such carriers.

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“We need testing because once we have a sense of who's infected, we can start moving from a uniform stay-at-home advisory and more rapidly return to normal life, with testing and checking in,” Bradnan said.

Even an imperfect test would be better than no home testing, Tabarrok said. On his site, Marginal Revolution, he has compiled information from several respected economists who ran the numbers and came to the same conclusion.

“At this point in time we need to unleash American ingenuity and enterprise and evolve our way to the frontier as conditions improve,” Tabarrok wrote.

Maxim Lott is Executive Producer of Stossel TV and creator of ElectionBettingOdds.com. He can be reached on Twitter at @MaximLott.