"If we require a test, people are going to say, 'What if we can't get a test?'"

Biden’s team insists they took what steps they could in the fall to build up testing capacity but acknowledge that a surge in demand and relatively recent emergency use authorizations from the US Food and Drug Administration have made stockpiling at-home tests a challenge.

Television footage of long lines at testing centers grabbed Biden’s attention over the Christmas weekend. And the shortage of tests factored into the administration’s decision Monday not to recommend tests for individuals exposed to the virus to emerge from a shortened five-day quarantine, according to an official familiar with the discussions.

“If we require a test, people are going to say, ‘What if we can’t get a test?’ ” the senior administration official said, recounting internal deliberations on condition of anonymity. “Rather than letting the perfect be the enemy of the good,” the official said, the US Centers for Disease Control and Prevention opted for less stringent language, noting that “best practice would also include a test for SARS-CoV-2 at day 5 after exposure.”