Antigen tests are “contagiousness” tests. They are extremely effective (>98% sensitive compared to the typically used PCR test) in detecting COVID-19 when individuals are most contagious. Paper-strip antigen tests are inexpensive, simple to manufacture, give results within minutes, and can be used within the privacy of our own home—the latter is immensely important for many people across the U.S.
The leading prototype for the antigen test I’m describing includes a small paper strip with a special molecule embedded on it that detects SARS-CoV-2 and turns dark when the virus is present in the sample. To use the test, the person gently swabs the front of their nose. They put the swab into a small pre-filled tube and drop a paper strip into the tube. Within minutes, the results are known based on whether a line shows up on the paper or not (much like a pregnancy test).
If only 50% of the population tested themselves in this way every 4 days, we can achieve vaccine-like “herd effects” (which is when onward transmission of the virus across the population cannot sustain itself—like taking fuel from a fire—and the outbreak collapses).