The Federal Emergency Management Agency opened its first Covid-19 mass vaccination sites on Tuesday, in Los Angeles and Oakland.
The centres are part of an effort by the Biden administration to administer shots more quickly and reach minority communities hit hard by the coronavirus outbreak.
Snow and icy weather across much of the US forced the cancellation of some vaccinations and threatened to disrupt deliveries over the next few days.
Houston’s public health agency lost power and had to scramble to give out thousands of shots before they were spoiled.
The US is administering an average of about 1.67 million doses a day, the Centres for Disease Control and Prevention said.
At the same time, deaths have gone down sharply over the past six weeks and new cases have dropped.
About 39.7 million Americans, or 12 per cent of the US population, have received at least one dose of the vaccine, and 15 million have had both shots, the agency said.
There are about 2,400 deaths a day on average, down by more than 900 from their peak in mid-January.
And the average daily number of new cases has dropped to about 85,000, the lowest in three and a half months.
That is down from a peak of almost a quarter million a day in early January. The overall US death toll is about 490,000.
In the early morning in LA, several dozen cars were already lined up with people sitting inside reading newspapers and passing the time, half an hour before the 9am opening of the country’s first mass vaccination site.
Troops in camouflage fatigues stood around the sprawling car park at California State University, where about 40 white tents were erected and dozens of orange cones put in place to guide traffic.
The site, set up in heavily Latino East Los Angeles as part of an effort to reach communities who have suffered disproportionately from the pandemic, aims to vaccinate 6,000 people a day.
Another such site opened at the Oakland Coliseum, near working-class black and Latino neighbourhoods.
California has overtaken New York state for the highest death toll in the nation, at more than 47,000.
The LA vaccination site is “proximate to a community that has been disproportionately affected by this pandemic", Governor Gavin Newsom said. “The effort here is to address that issue forthrightly.”
The Biden administration intends to establish 100 federally assisted vaccination sites nationwide in co-operation with state authorities.
Meanwhile, the coronavirus put a dampener on Mardi Gras in New Orleans.
The French Quarter’s Bourbon Street, where the rowdiest and bawdiest partying usually takes place, was blocked off with police barricades and bars were ordered to close.
“It’s hard to wrap my head around it,” New Orleans lawyer Dave Lanser, wearing a luminescent green cape and a black mask with a curved beak, said as he looked up and down a near-empty Bourbon Street.
“I don’t think there’s a way to safely do it this year. So I support cancelling the parades, closing the bars, all that kind of stuff. It’s just kind of the reality of it.”
Mardi Gras crowds last year were blamed for a severe outbreak of Covid-19 in Louisiana.
Snow, ice and bitter cold forced the cancellation of vaccinations in places including Memphis and Missouri.
Houston’s Harris County rushed to dispense more than 8,000 doses of Moderna’s coronavirus vaccine after a public health centre lost power early on Monday and its backup generator also failed, authorities said.
The shots were distributed at three hospitals, Rice University and the county jail.
“It feels amazing. I’m very grateful,” said Harry Golen, 19, a student who waited nearly four hours with his friends, much of it in the frigid cold.
He was among the last to receive shots, which otherwise would not have reached students until March or April.
More than 400,000 more vaccine doses due in Texas will now not arrive until at least Wednesday, officials said.
The Biden administration said the severe weather is expected to disrupt shipments from a FedEx centre in Memphis and a UPS installation in Louisville, Kentucky.
Both serve as vaccine shipping centres for several states.
The administration is increasing the amount of vaccines sent to states to 13.5 million doses a week, a 57 per cent increase from when Mr Biden took office about a month ago, White House press secretary Jen Psaki announced.
Ms Psaki also said the administration is doubling to 2 million doses a week the amount of vaccine being sent to pharmacies across the US as part of a programme to improve access in neighbourhoods.
