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Are most "in home" COVID tests a joke? FDA doing anything?

The FDA’s Covid Contradictions: At-Home Test Edition

It has eased standards for vaccines, for all ages, while limiting access to tests that would reduce spread.

Allysia Finley, WSJ

March 5, 2023 3:42 pm ET

A friend recently woke up with a sore throat. He took an at-home Covid test, which came back negative, then went to work and a happy hour with two colleagues. Several days later he learned they developed symptoms and tested positive for the virus. Did he have a false negative and infect them?

It seems likely, but it’s impossible to know. Many Americans have probably had similar experiences. At-home Covid tests were supposed to help people who came down with cold or flulike symptoms determine whether they should isolate or seek treatment—but their utility has been greatly diminished by frequent false negatives.

One study published last spring in the Journal of the American Medical Association found that at-home tests detect only 64% as many cases as PCR tests taken on the same day, and only 10% of the asymptomatic cases. They often yield false negatives during the first few days after infection when people are most contagious.

Much of the blame lies with the Food and Drug Administration, which has prioritized minimizing false positives over false negatives. There is usually a trade-off between the two results in the development of medical diagnostic tests—adjusting the formula in rapid tests to minimize one will usually result in more of the other.

The FDA specifies that at-home tests should demonstrate merely 80% sensitivity in clinical trials—that is, less than 20% of people who are truly positive test negative—though they typically fare worse in studies from the real world. At the same time, the agency says tests should be at least 98% specific, meaning less than 2% of people who are truly negative test positive.

As a case in point, the FDA has refused to authorize a test by the startup Global Diagnostic Systems, which yielded no false negatives in clinical trials but had a 5.2% false-positive rate. The test uses a high-absorption swab and highly sensitive antibodies to detect the Covid antigen. Its process also doesn’t dilute the sample and produces an easy-to-read test line for positive results.

By contrast, other tests require users to put their swab into a buffer and either squeeze the sample from the swab or add drops to it. These approaches dilute the sample and make it more difficult to detect if Covid is present. Users may also miss very faint lines on test strips.

Abbott’s BinaxNOW test instructions, for example, place a magnifying line next to its test strip and advise users to “look very closely” because “the bottom line can be very faint.” Abbott says that eight of 30 users in its “human factors” study struggled to see some results: “As the line intensity became fainter, the ability to read the result correctly ranged from 83% to 60%, with an overall rate of 70%.”

Thanks to its relative ease of use, the Global Diagnostics test should also be less likely to yield false negatives in the real world. GDS shared with the FDA a modeling study by Yale researchers that showed the test would result in far fewer infections than other tests under various epidemiological and behavioral assumptions.

Why, then, won’t the FDA relax it specifications and green-light the test? An FDA spokesperson says the agency “cannot comment on any submissions that a company may or may not have made.” As a general matter, though, the agency is worried about false positives delaying a correct diagnosis and treatment for the actual cause of illness. Someone who gets such a result might also quarantine with others who are infected.

The latter scenario is probably uncommon and would put only the noninfected at risk. On the other hand, false negatives could also delay treatment for people who are at risk of getting severely ill with Covid. Treatments such as the antiviral Paxlovid are more effective when taken soon after symptoms start.

False negatives contribute more to virus spread and put vulnerable people at risk. The FDA has acknowledged tacitly that the high rate of false negatives is a problem. In November the agency instructed people who test negative to do multiple tests over three to five days to increase the odds of detecting the virus. But people can hardly be expected to isolate and repeatedly test themselves over several days every time they develop cold symptoms.

This strategy is also expensive. After the public-health emergency ends in May, Americans will have to start paying out of pocket for at-home tests, which cost about $10 each. Manufacturers make more money by producing less-sensitive tests that must be taken repeatedly. But many people would prefer tests that yield fewer false negatives even if they have a slightly higher risk of delivering a false positive. Why not give them the choice?

The FDA has eased its standards to authorize Covid vaccines for children and bivalent booster shots despite potential risks and scant evidence of benefits—all while limiting access to at-home tests that could reduce virus spread and help protect at-risk Americans. Once again, public-health officials appear oblivious to their contradictions.

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