Coronavirus updates: Herd immunity by fall 'ambitious,' says surgeon general nominee

U.S. President-elect Joe Biden and Vice President-elect Kamala Harris honored the 400,000 Americans who have died from COVID-19 with a tribute in front of the Lincoln Memorial Reflecting Pool in Washington, D.C. on Tuesday evening.

The 400 lights along the pool were lit to symbolize the lives lost to the virus.

At the ceremony, part of the incoming administration's inaugural festivities, Harris called on Americans to "grieve and begin healing together."

"Though we may be physically separated, we, the American people, are united in spirit," she said.

Emirates Airlines and Etihad Airways said they have partnered with the International Air Transport Association to trial IATA Travel Pass -- a mobile app that serves as a “digital passport” to verify pre-travel COVID-19 testing or vaccination status.

The app also helps passengers find information on travel and entry requirements at their destinations.

Emirates Airlines said it plans to roll out the first phase in April, during which passengers leaving Dubai can share their COVID-19 test status directly with the airline through the app before arriving at the airport. Etihad will first offer the travel pass on some flights out of Abu Dhabi in the first quarter of 2021.

ABC News’ Christine Theodorou contributed to this report.

The United Kingdom reported a record 1,610 new fatalities from COVID-19 on Tuesday, bringing the country's weekly death toll to 8,267 -- a 19.8% increase over the previous week.

The U.K. -- an island nation of 66 million people made up of England, Scotland, Wales and Northern Ireland -- has the fifth-highest number of confirmed deaths from COVID-19 worldwide, behind the United States, Brazil, India and Mexico, according to a count kept by Johns Hopkins University.

Despite the record death toll, the daily number of new cases is on the decline in the U.K. amid national lockdowns. The U.K. reported 33,355 new cases on Tuesday, bringing the weekly total to 302,802 -- a 22.3% decrease from the last week.

ABC News’ Christine Theodorou contributed to this report.

The U.S. death toll surpassed 400,000 on Tuesday and now stands at 400,022 fatalities.

The number of American lives lost to the coronavirus is more people than the number of U.S. soldiers who died in battle during World War I, World War II and the Vietnam War combined, according to a data estimate compiled by the Department of Veterans Affairs.

The U.S. death toll is roughly equivalent to the population of Tampa, Florida, or Tulsa, Oklahoma.

By the middle of February, "we expect half a million deaths" in the U.S. from COVID-19, Dr. Rochelle Walensky, who’s nominated to serve as the next director of the Centers for Disease Control and Prevention, told CBS’ "Face the Nation" on Sunday.

ABC News’ Arielle Mitropolous contributed to this report.