Editor’s Note (9/29/20): This story has been updated and republished in light of the Trump administration’s newly announced plans to ship millions of antigen tests to states and vulnerable communities.
An inexpensive coronavirus test that millions of Americans could use at a pharmacy, in a workplace or even at home could prove to be a vital asset in allowing people to return to jobs and school. Deborah Birx, the White House’s coronavirus-response coordinator, has called rapid antigen tests the “breakthrough innovation” that is needed to perform hundreds of millions of such assays a day. The remarks echoed her previous statements that antigen tests might be used to examine broad swaths of the public.
The technique often involves a technology—called a lateral flow assay—similar to that employed in home pregnancy tests. In the test, an antibody can bind to one of the spike proteins (the antigens) that cover the surface of the virus like the spines on a puffer fish. The tests are inexpensive to produce and simple to use, and they deliver results in minutes. On September 28, several months after this story was originally published, the Trump administration announced a plan to distribute 150 million of these assays, developed by Abbott Laboratories. The test, called BinaxNOW, correctly identifies 97.1 percent of positive cases and 98.5 percent of negative cases, and it provides results in 15 minutes. An Abbott spokesperson declined to comment on the record about the test’s accuracy.
The goal is also to field a test that is just as accurate as the current standard, which uses polymerase chain reaction (PCR) to process the virus’s genetic material and amplify it for detection. But major technical hurdles still remain. “What you would want in terms of a breakthrough is that [an antigen] test is more sensitive, [or less prone to false negatives], and easier to use than a PCR-based test. And that is not so easy to do,” says Bettina Fries, chief of the infectious diseases division at Stony Brook Medicine. “Normally, PCR-based tests are more sensitive.”
The urgent need to conduct massive levels of testing means that any feasible technology is being considered. OraSure Technologies, a medical device company in Bethlehem, Pa., received a $710,310 federal contract last month for an in-home assay that can potentially detect a coronavirus antigen in saliva in as little as 20 minutes. Stephen Tang, the company’s CEO, says such antigen tests are needed to screen millions of people per day. “You can’t be dependent on the throughput of laboratories and the availability of medical and laboratory professionals,” as PCR assays typically require, to conduct widespread testing, he says.
Because a PCR test makes thousands of copies of its target RNA, it is able to detect a virus at far lower concentrations, called the limit of detection, than antigen tests typically can. PCR’s limits of detection “are on the order of a few hundred virus particles in a milliliter of transport liquid,” says Geoffrey Baird, acting chair of laboratory medicine at