The F.D.A. announced Monday that it would allow the sale of an antigen test known as Flowflex. The test has been available in Europe but not here, even though the company that makes it — Acon Laboratories — is based in San Diego.

The decision suggests that the F.D.A. has become willing to approve other rapid tests too, Alex Tabarrok, an economist at George Mason University and an advocate of expanded testing, told me. Separately, the Biden administration plans to announce an expansion of rapid testing today, a White House official told me last night. It will be a $1 billion government purchase of tests, meant to accelerate their production, on top of other money the administration has already dedicated to rapid tests.

Together, these moves will quadruple the number of rapid tests available to Americans by early December, the official predicted. Some of the tests will be free (as many tests are in Europe, thanks to government subsidies), available at one of about 20,000 pharmacies or 10,000 community clinics nationwide. Others will be for sale at retailers.

Until now, antigen tests — like the ones CVS sells — have typically cost about $12 each in the U.S. The coming influx of supply should cause the cost to fall, allowing antigen tests to become a bigger part of this country’s Covid response.