President Joe Biden will announce a plan on Tuesday 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.

Biden's new efforts come as the omicron variant became the most dominant COVID strain in the country Monday, accounting for nearly three-quarters of all cases, and just as travel kicks off at nearly pre-pandemic levels for the holiday season.

The free at-home rapid tests will be delivered by mail to Americans who request them, a senior administration official told reporters on Monday night in a preview of the speech, marking a slightly different approach from European countries that chose to send tests to all residents.