A representative-elect from Louisiana has died of Covid-19, the first member of the US House of Congress to succumb to the disease.
Republican Luke Letlow, 41, had been elected to Louisiana's 5th district and was due to be sworn in on Sunday.
"It is with heavy hearts that @FirstLadyOfLA and I offer our condolences to Congressman-elect Luke Letlow's family on his passing after a battle with COVID-19," Louisiana governor John Bel Edwards tweeted.
"I am heartbroken that he will not be able to serve our people as a U.S. Representative, but I am even more devastated for his loving family," Mr Edwards said.
Mr Letlow is survived by his wife, Julia Barnhill Letlow, and two young children.
"The family appreciates the numerous prayers and support over the past days but asks for privacy during this difficult and unexpected time," his family said in a statement to US media. "A statement from the family along with funeral arrangements will be announced at a later time."
Mr Edwards said he has ordered flags to be flown at half-staff on the day of Mr Letlow's funeral.
Mr Letlow had announced on 18 December that he had tested positive for Covid-19 and was quarantining at home. He was hospitalised three days later.
Mr Letlow is the first member of the US Congress to die of Covid-19.
New Covid-19 variant detected for first time in US
Meanwhile the new variant of coronavirus has been detected for the first time in the United States and Latin America as President-elect Joe Biden vowed to significantly ramp up the vaccination drive.
The new strain, which first emerged in the UK, pushed Britain to a new daily record of infections and led South Africa to impose a raft of new measures, amid fears around the world that holiday revelers are aggravating the spike in infections.
The EU health agency warned the strain carried a high risk for more hospitalisations and deaths - not because the infections are more severe but because it spreads more easily.
The state of Colorado recorded what is believed to be the first case in the US - which has suffered the highest death toll of the year-old pandemic that has claimed more than 1.78 million lives globally. Nearly 338,000 people have died of Covid-19 in the US.
Governor Jared Polis said a man in his 20s near Denver was infected with the variant known as B.1.1.7 and is isolating.
Mr Biden, after a briefing from experts, warned that the dire Covid situation may not ease up until "well into March".
"The next few weeks and months are going to be very tough - a very tough period for our nation, maybe the toughest during this entire pandemic," he said.
Hospitalisations are back at an all-time high in the US at more than 121,000 as of Monday.
In Los Angeles, ambulances waited all day to unload Covid patients, with more than 95% of hospitals forced to divert new cases away, and one reportedly treating patients in its gift shop and chapel. Southern California extended a three-week-old lockdown indefinitely yesterday.
Mr Biden called mass vaccination the "greatest operational challenge we've ever faced as a nation" - and promised the US would do better after he replaces defeated President Donald Trump on 20 January.
"The Trump administration's plan to distribute vaccines is falling far behind," Mr Biden said, promising: "I'm going to move Heaven and Earth to get us going in the right direction."
The Trump administration had predicted that 20 million Americans would be vaccinated by the end of December.
With days left, some 2.1 million have received the first shot of the vaccine, according to the Centers for Disease Control and Prevention.
Mr Biden renewed his promise to administer 100 million vaccine doses in his first 100 days in office and confirmed he would invoke a Korean War-era law to force private industry to step up production.
Record cases in Britain
Britain's government came under pressure to tighten restrictions as it announced a record 24-hour high of 53,135 new infections.
Critical care doctor Samantha Batt-Rawden said medical staff were at "breaking point".
"We are incredibly thin on the ground. NHS (National Health Service) staff have not been prioritized for the vaccine and are going off sick in droves with the new strain," she tweeted.
In South Africa, which has recorded more than 300 cases of the new variant and is the first African nation to hit one million cases, the government banned the sale of alcohol and made masks compulsory in public.
"We have let down our guard, and unfortunately we are now paying the price," said President Cyril Ramaphosa.
Chile yesterday became the first Latin American country to detect the new strain, in a woman who returned from Madrid after also visiting Britain and Dubai.
In response, health authorities announced a ten-day quarantine from 31 December for all arrivals.
The new strain was also detected in the United Arab Emirates and India, which has the second-biggest caseload in the world.
Worrisome trends have been increasing worldwide, with South Korea - hailed for its early success - logging its highest daily death toll yet.
And Moscow reported a 27% increase in fatalities in the capital from October to November -- a day after Russia admitted its number of Covid-19 deaths were more than three times higher than previously reported.