Biden offers more free coronavirus tests although demand has slowed.

The Biden administration on Tuesday formally began allowing Americans who had ordered free coronavirus tests this winter to request a second round of four tests per household, through the same U.S. Postal Service program that President Biden unveiled in January.

The move, which Mr. Biden had promised last week during his State of the Union address, followed a crush of interest in the program when it debuted in January. At the time, case rates had skyrocketed because of the Omicron variant and tens of millions of households scrambled to obtain the free tests.

Now, with supply outpacing demand and virus cases on a steep decline, White House officials and public health experts say it will require significant effort to sustain interest in testing — and ensure that manufacturers keep producing tests.

“People were able to sell tests like hot cakes over Omicron,” said Gigi Gronvall, a testing expert at Johns Hopkins University. “They were able to gouge prices. It’s now, when the libraries can’t give them away, that the government needs to make sure that the manufacturers don’t pull out, like what happened before Delta.”

The supply of rapid at-home tests has ballooned in recent weeks. Federally authorized manufacturers had the ability to make an estimated 535 million tests last month and 462 million this month, said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University who is also on the board of OraSure, which makes rapid virus tests.

Tests are now easier to find in pharmacies and at many community sites. And the majority of American households ordered free tests from the Postal Service website over the last seven weeks, said Dr. Tom Inglesby, the White House’s testing coordinator. More than 275 million tests have been delivered to nearly 70 million households, with more than 5,000 Postal Service employees in fulfillment centers packing and shipping them.