RE: Why rapid tests are needed8 Aug 2020 19:46
A good article on this in the current issue of Science
https://science.sciencemag.org/content/369/6504/608
An extract below giving an idea of the number of tests needed in US
'Antigen tests, which immobilize antibodies on a test strip, promise an even greater speedup. Those antibodies detect viral proteins in saliva or a nasal swab. Such tests cost as little as $1 to $2 each, give a yes/no readout within minutes, much like a pregnancy test, and are already used to detect influenza, HIV, and other viruses. Two companies—Quidel Corporation and Becton, Dickinson and Company (BD)—have received emergency use authorization from the U.S. Food and Drug Administration to sell antigen tests for SARS-CoV-2. Other companies have similar tests in the works.
Because antigen tests don't amplify viral material but simply detect what is present in the sample, they are less accurate than PCR. Some antigen tests correctly detect only one-half to three-quarters of infections. But they could still be a valuable health tool if performed often enough; few infected people would be missed in multiple rounds of tests. And people who receive a positive antigen test could be isolated and retested with a PCR test to confirm the result.
Among the hurdles facing widespread, repeat screening is the scarcity of such tests. Quidel and BD together manufacture about 3 million antigen tests per week. But a national screening strategy would likely require 25 million fast tests or more, says Jonathan Quick, who heads pandemic response for the Rockefeller Foundation. On 16 July, the foundation released a national COVID-19 testing plan calling on the federal government to spend $75 billion on providing 30 million screening and diagnostic tests per week.
Quick says companies are reluctant to ramp up production dramatically if they are unsure of the market for the products. One solution, he adds, could be a promise by the federal government to buy tens of millions of tests, much as it has done with vaccine doses. In one such effort, the governors of six U.S. states announced this week they are banding together to ask Quidel and BD for a total of 3 million tests.'