Tennessee has emerged alongside California as an epicentre of the latest COVID-19 surge even while more than one million Americans have been vaccinated as US political leaders sought to guard against a highly contagious coronavirus variant sweeping across Britain.
Tennessee averaged nearly 128 new infections per 100,000 people over the last week, the highest of any US state, according to US Centers for Disease Control and Prevention data. California stood second at 111 new cases per 100,000 residents.
"Our state is ground zero for a surge in COVID-19 and we need Tennesseans to (do) their part," Governor Bill Lee said on Twitter, urging residents to wear face masks and gather only with members of their own household over Christmas.
Some public health officials say Americans' travelling and gathering for Thanksgiving contributed to the latest nationwide explosion in cases.
All told, 31 US states have reported a grim record in new COVID-19 infections for December as hospitalisations and deaths also spiral. More than 194,600 new cases were confirmed on Tuesday alone.
The CDC said that as of Wednesday morning more than one million people nationwide had been given the first of the two doses required for the two coronavirus vaccines that have been approved.
But most Americans have been told that it could be six months or more before they are eligible for the shots as priority is given to healthcare workers, nursing home residents and in some cases top government officials.
Health and Human Services Secretary Alex Azar and Dr. Anthony Fauci, the top US infectious disease official, received the Moderna vaccine on live television on Tuesday. President-elect Joe Biden was inoculated with the Pfizer/BioNTech vaccine in front of cameras on Monday.
The Trump administration said on Wednesday it had reached a $US2 billion ($A2.6 billion) deal with Pfizer to distribute 100 million additional doses of its vaccine by July.
But Americans who saw a ray of hope in the release of the two vaccines in December learned of an even more transmissible coronavirus variant spreading in the United Kingdom.
Drug makers Pfizer and Moderna were testing their vaccines against the variant, but believed the drugs would be effective against the mutant virus.
The United States, unlike many nations worldwide, has not banned travellers from Britain.
New York City Mayor Bill de Blasio said the city would order international travellers to quarantine for 14 days on arrival and provide contact information to government officials. Sheriff's deputies will make visits to enforce the order on those arriving from Britain, the mayor said.
Travellers found to violate those orders face fines of $US1000 ($A1300) per day, de Blasio said.
New York Governor Andrew Cuomo has asked airlines to screen British travellers for COVID-19. The state was an early epicentre of the virus and has recorded more than 36,000 COVID deaths, far more than any other state.
Washington state Governor Jay Inslee this week ordered a 14-day quarantine for travellers arriving from the UK, South Africa or other countries where the new variant had been detected.
In New York City, vaccination programs expanded to the Fire Department, where roughly 6000 personnel have contracted the virus, Fire Commissioner Dan Nigro told reporters.
Some 400 FDNY paramedics lined up to receive their first doses of the Moderna vaccine on Wednesday, including Verena Kansog, advanced life support coordinator for Manhattan, who got her shot at a training centre on Randalls Island.
"I feel relieved," Kansog, who worried about bringing the disease home to her elderly mother, told Reuters in a phone interview. "I was not one single bit nervous."