In sharp contrast lie the “instant coffee” rapid paper antigen tests, including those made by E25Bio and Sherlock Biosciences, and one under development by 3M and MIT. These are fast, simple to use, at-home tests, and some are really inexpensive: about $1 to $5 per test. They are called lateral flow assays, but manifestly they are paper-strip tests that have an antibody embedded on filter paper. If a saliva sample has coronavirus present, the antibody will bind that viral antigen, turning the test positive, much like a pregnancy test works. Though the tests have much lower sensitivity than PCR tests overall, one advantage they have is that they do not detect leftover, inactive viral RNA particles, which may be present days to weeks after a person is infectious.
Here’s the key: What is more important than a perfect test is one that turns positive during the time period in which an individual can spread the virus to others—and that’s, purportedly, what these cheap tests do well. Generally, disease transmission in COVID-19 is believed to begin early—several days before one becomes symptomatic. Viral load levels peak early and then they gradually decline, with an individual unlikely to be infectious approximately eight to 10 days after showing symptoms.
Source: ‘Instant Coffee’ COVID-19 Tests Could Be the Answer to Reopening the U.S. – Scientific American
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