Meryl Williams Clark watched this summer as coronavirus cases caused by the delta variant rose, sickening people she knew. Her 8-year-old stepson was about to start attending class in-person at a school with no mask mandate.

Worried about the increased cases and an unvaccinated child, Clark, a communications coordinator in West Virginia, went to a local Walgreens and bought some at-home coronavirus tests.

“I grabbed a couple, but after the school year started, they were sold out everywhere,” she said in an interview.

Williams Clark, 35, is not alone: In recent months, it has been difficult to find at-home coronavirus tests, particularly the rapid antigen tests found online and at most drugstores. Some retailers have sold out of the tests or limited the number that people can buy; others have warned customers that even when the tests are available, deliveries may be delayed due to high demand.

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The clamor for the tests, which include Abbott’s BinaxNOW, Ellume’s Covid-19 Home Test and Quidel’s QuickVue, has increased as many states experienced a surge in COVID-19 cases at the same time that the number of professional testing sites were dwindling. As more people head back to the office, send their children to school and start to socialize more – even with the threat of the highly contagious delta variant looming – these tests give many people peace of mind.

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To match the demand, the Biden administration announced last month that it would buy $1 billion worth of at-home tests, a move that could quadruple the number of tests available to the public by December.

President Joe Biden said in a speech in September that Walmart, Amazon and Kroger will sell at-home rapid test kits at lower costs — up to a 35% discount — for three months. The tests have been averaging about $24 per kit, though prices are starting to drop at some retailers.

Infectious-disease experts and epidemiologists have said that the investment in the tests is long delayed, and that they can be an effective tool in curtailing the spread of the coronavirus as winter nears and opportunities to gather outside shrink.

The scarcity of at-home tests is the result of large organizations and schools purchasing tests in efforts to return to a level of normalcy and a slow regulatory process for at-home test approval, said Neil J. Sehgal, assistant professor of health policy and management at the University of Maryland School of Public Health.

Sports stadiums, concert halls and colleges and universities purchased tests in bulk in the spring, preceding public demand, he said.

“In the U.S., we’ve been thinking about rapid tests the wrong way and regulating them like medical devices,” he said, comparing accessibility of tests to countries such as Germany and the United Kingdom. “It’s a public health intervention. Medical standards of approval really slow down the approval process.”

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The Biden administration announced last month that it is taking additional steps to speed the authorization of at-home tests. A $70 million investment by the National Institutes of Health will help manufacturers navigate the Food and Drug Administration’s regulatory process.

An FDA official pushed back on the notion that the agency is moving at a slower pace than other parts of the world, noting that the United States was among the first countries in the world to authorize at-home coronavirus tests last year.

Germany and the United Kingdom invested billions of dollars in at-home testing – long before Biden and the Department of Health and Human Services announced their substantial backing of making at-home coronavirus tests more accessible. That earlier investment made it easier for those nations to scale up manufacturing at-home tests.

“The difference is really in economics,” the official said.

Before the delta variant took over, coronavirus case numbers were dropping in the United States and demand for tests declined – along with the closing of at-home coronavirus test manufacturing sites, the official said.

At-home tests can provide valuable information but should not be considered a pass, experts said; they simply tell a person whether he or she is infected with detectable amounts of the virus at the moment the test is taken. Instead, the tests should be used as one tool in a tool kit to help prevent the spread of the coronavirus, along with vaccination and, when appropriate, face masks.

Federal health authorities recommend that people — vaccinated or not — should get tested if they have symptoms of COVID-19, which include headache, fatigue, fever, body aches, cough, breathing difficulties, and loss of taste or smell. Matt Binnicker, director of clinical virology at Mayo Clinic, said at-home tests are most accurate when the person is symptomatic because that’s when the virus will be present at the highest levels and, therefore, the easiest to detect.

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The Centers for Disease Control and Prevention said fully vaccinated people who do not have symptoms should still get tested three to five days after potential exposure, and that those who are not fully vaccinated should get tested immediately and then again five to seven days later. In addition, some experts said there are certain circumstances in which it may make sense for people to get tested as a precaution, even when they are asymptomatic and have not knowingly been exposure to the virus, such as when a person is planning to visit someone who is unvaccinated or at higher risk for severe disease.

For those who need a test, there are two types used to diagnose current infections – molecular tests and antigen tests.

Antigen tests – the 15-minute tests done at home – are usually faster but less able to detect small amounts of the coronavirus. Molecular tests, namely polymerase chain reaction (PCR) tests, are much more sensitive. PCR tests are designed to look for evidence of viral RNA – the genetic material of the coronavirus. And because these sensitive tests are capable of detecting mere fragments of RNA – not the whole active virus required to infect others – the tests can come back positive for a while, as the human body can shed viral RNA while it is eliminating the virus, said Jennifer Nuzzo, lead epidemiologist for the Johns Hopkins Covid-19 Testing Insights Initiative.

That why some scientific researchers prefer antigen tests – the faster, sometimes less accurate tests that can be done at home. Nuzzo said the fact that antigen tests are less sensitive to smaller amounts of viral RNA that can be found in the noses of people who are no longer contagious “may be a feature rather than a defect.” Also, she said, these tests can be easily repeated to confirm negative test results.

As more antigen tests become available, it’s important for consumers to consider which tests are appropriate for them, said Jennifer Smith, associate professor of epidemiology at the University of North Carolina at Chapel Hill’s Gillings School of Global Public Health.

Smith said it’s important for consumers to read the packaging and inserts for information about for whom the test is intended.

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“The most important thing is for people to ask: ‘Who is that test for?’ Are you that person? Are you eligible to be that person?” Smith said. “Do you know what symptoms are allowed, and do they provide you that information? If it’s a no and it’s not meant for you, you can’t rely on test performing well.”

But Binnicker cautioned that when people are using the at-home rapid antigen tests as a screening tool, they should use the test exactly as directed, waiting four to five days after potential exposure to take the test and, in some cases, taking two tests several days apart.

When a person tests negative, experts said the test should be repeated in a few days to ensure the most accurate result.

When a person tests positive, some of the experts said the person should go get a PCR test from a medical facility to confirm the results, and all agree the person should establish contact with a health-care professional.

Williams Clark said she has about five boxes of tests at home as a precautionary measure. When her stepson had been exposed to COVID, having the tests on hand to confirm that the family wasn’t infectious offered her quick answers at a time of uncertainty.

She plans on testing herself this week before she travels for the first time in over a year for a job and once she returns, she said.

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“I see the at-home test as a first step and first line of events,” she said. “Having these on hand just is kind of relief for that.”

At times, she feels torn about having a small stash on hand and thinking about buying more when they’re available online, because she doesn’t want to be “hoarding” supplies, she said.

From a public health standpoint, the privacy of at-home tests could pose a problem because cases of the coronavirus detected at home may not be reported to health-care professionals and recorded in surveillance numbers.

“It’s really important to get a swab collected for a lab-based test that same day or the next day so that you can confirm the result and so that positive result gets tracked by public health,” Binnicker said. He added that it is also important to be connected with a physician “in the event that the patient needs to be treated with any medications to help prevent them from having a severe outcome.”

Health experts said that at-home rapid tests are a useful tool and that the move by the Biden administration to guarantee testing supplies is commendable. But some have concerns that the timetable and quantity of test kits may not be enough to help get control of the pandemic.

Michael Mina, assistant professor of epidemiology at Harvard T.H. Chan School of Public Health, said that although vaccines have been effective at preventing severe disease, hospitalization and death, “we still need to stop transmission.”

“What rapid tests do is they allow us to live more peacefully with this virus – to actually be able to not have it be so disruptive to society,” said Mina, who has been researching the tests. For example, he added, rapid tests could abolish the need for quarantine “to keep students in school, to keep businesses running and to stop the need for shutdowns, even amid outbreaks.”

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