WASHINGTON (AP) — President Joe Biden is betting on millions more rapid, at-home tests to help curb the latest deadly wave of the COVID-19 pandemic, which is overloading hospitals and threatening to shutter classrooms around the country.

But the tests have already disappeared from pharmacy shelves in many parts of the U.S., and manufacturers warn it will take them weeks to ramp up production, after scaling it back amid plummeting demand over the summer.

The latest shortage is another painful reminder that the U.S. has yet to successfully manage its COVID-19 testing arsenal, let alone deploy it in the type of systematic way needed to quickly crush outbreaks in schools, workplaces and communities.

Experts say encouraging signs last spring led to false confidence about the shrinking role for tests: falling case numbers, rising vaccination rates and guidance from health officials that vaccinated people could largely skip testing. Officials recently reversed that advice as cases and deaths driven by the delta variant surged anew.

"For all of us, there was a combination of optimism and hubris in the June timeframe that led us believe this was over," said Mara Aspinall, a health industry researcher at Arizona State University who has become a leading authority on COVID-19 testing supplies.

Colorado's Mesa County is among the local governments that have stopped offering rapid tests as part of their free testing programs for the general public.

"We were seeing shortages in the tests across the county, so we are really prioritizing supplies for our school districts to have quick turnaround for testing, to help them if needed," said Stefany Busch, a county spokeswoman. She noted that tests that are processed in laboratories — which take longer to give results — remain plentiful.

Indeed, parts of the U.S. testing system are faring better than during prior surges. The large commercial labs that process the majority of tests performed at hospitals and testing sites still report plenty of capacity. LabCorp, one of the biggest laboratory chains, said last week it was delivering results for 150,000 tests daily, with the ability to double that number.

Still, rapid tests have a clear advantage in that they can be done anywhere and have a 20-minute turnaround time, but most school testing programs still rely on tests processed in labs, which return results in a day or two.

In general, the U.S. has been far more cautious about embracing rapid, at-home testing technology compared to countries like Britain that have rolled it out widely. The Food and Drug Administration has authorized only about a half-dozen such tests, compared with more than 400 laboratory tests. Many experts, including FDA regulators, still consider laboratory technology the "gold standard" for accuracy because it can detect even minute levels of virus in the nose.

But in his speech this month announcing sweeping new vaccine mandates, Biden highlighted rapid tests, saying the government would purchase 280 million of them, as he also called on all schools to set up regular testing programs. Biden said the federal government will use the Defense Production Act to ensure manufacturers have the raw materials they need to make tests.

If those plans sound familiar, it's because they were part of Biden's original strategy for dealing with COVID-19 released in January.

A spokeswoman for the Department of Health and Human Services said the latest actions "build on earlier initiatives" as the delta variant-driven surge boosts testing demand.

HHS has announced few details of the $2 billion-plan to purchase rapid tests. For now, retail chains like CVS and Walgreens have placed limits on how many at-home tests customers can buy.

Abbott Laboratories — the country's largest rapid test maker — said it is currently producing "tens of millions" of its BinaxNOW tests per month and working to increase capacity in coming weeks.

The New York Times recently reported that over the summer Abbott shut down one of its factories, laid off employees and destroyed some testing components.

Abbott said those decisions came after vaccinations climbed and demand for testing plunged. The destroyed supplies had limited shelf life and were not viable for sale in the U.S. or for donation overseas, according to Abbott.

"It is now very clear that testing is a necessary companion to vaccines and Abbott is ramping up again," said a company spokesperson.

The Biden administration's purchase plans should help stabilize supplies. But testing experts said the government could have stepped in months ago.

"We can't let the market determine our testing supplies, which is what happened here," said Scott Becker of the Association of Public Health Laboratories. "These tests are essential for public health purposes, so we have to have supply at all times."

Becker's group and others have seen testing demand increasing for weeks. And while labs are still operating well below levels seen last winter, there are unknowns, including how Biden's push for increased testing at schools and workplaces will impact them.

Testing policies vary widely by schools and states. Some districts regularly screen all students — including in Los Angeles, Baltimore and San Antonio. But many more districts do no testing at all.

A recent survey of 100 large districts found fewer than 15% required any testing for students. That's despite $10 billion in federal funds made available last spring to set up testing programs.

Many districts said the benefits of frequent testing didn't outweigh the logistical headaches of setting up programs and quarantining students. Some states even attempted to return testing funds to the federal government.

The Biden plan has no penalties for schools that don't test, a factor that may limit uptake.

To make rapid tests more affordable big retailers like Wal-Mart and Kroger have agreed to sell them at a 35% discount for the next three months. But the cheapest test — Abbott's BinaxNOW — would still sell for about $15 for a two-pack, out of reach for some families looking to frequently test themselves.

Other tests will cost $35 or more even after the discount.

That's far different from countries like the Britain and Germany that either distribute rapid tests for free or for prices in the low single digits.

But with the federal government investing billions in rapid tests, testing advocates are hopeful that more options — and cheaper ones — could eventually hit the market.

"When you're not winning a war you need to change your strategy, and I think this is a terrific first step to do that," said Aspinall.

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This story has been updated to correct the name of Becker's group to the Association of Public Health Laboratories.

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Follow Matthew Perrone on Twitter: @AP_FDAwriter

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute's Department of Science Education. The AP is solely responsible for all content.