WASHINGTON — President Biden announced on Tuesday a new plan to distribute 500 million free at-home rapid tests to Americans beginning in January as part of an attempt to double down on the spread of a transmissible variant that has hit the U.S. distressingly close to the holidays.

“I want to start by acknowledging how tired, worried and frustrated I know you are,” Biden began in his address to the nation from the White House. “For many of you, this will be the first or even the second Christmas, we look across the table to see an empty kitchen chair.”

“If you’re not fully vaccinated, you have good reason to be concerned,” Biden went on, talking about the rise of the omicron variant. “Almost everyone who has died from COVID-19 in the past many months has been unvaccinated. Unvaccinated.”

The Biden administration’s free at-home rapid tests will be delivered by mail to Americans who request them, Biden said, marking a slightly different approach from European countries that chose to send tests to all residents.

Americans will have to request the tests through a website that will launch in January. It is not yet clear how many tests Americans will be able to request per household.