WASHINGTON (AFP) - US health officials Sunday (Dec 6) expressed alarm over the refusal of many Americans to wear masks as the nation faces a soaring daily Covid-19 death toll and Donald Trump held a packed rally where basic health measures were flouted.

With the rollout of new vaccines expected in just weeks, the officials warned against false confidence - particularly with year-end travel still ahead.

Deborah Birx, coordinator of the White House coronavirus task force, said it was "frustrating" to hear people "parroting back that masks don't work (and) that gatherings don't result in superspreading events."

"This is not just the worst public health event. This is the worst event that this country will face," Birx told NBC's Meet the Press. "The vaccine is critical," she said, "but it's not going to save us from this current surge."

Health and Human Services secretary Alex Azar confirmed Sunday that the government expects 20 million people to receive vaccines from manufacturers Pfizer and Moderna by year's end - assuming the Food and Drug Administration approves them this week.

Moncef Slaoui, who heads the federal vaccine program Operation Warp Speed, told CBS that vaccinations could begin with 36 hours of FDA approval.

But experts expressed exasperation that many Americans continue to ignore guidance to wear masks, practice social distancing and avoid large crowds.

'Grim' weeks lie ahead

Former FDA commissioner Scott Gottlieb predicted the US death toll, now just over 280,000, could hit 400,000 by late January.

"There is a grim future ahead of us for the next six weeks," he told CBS's Face the Nation. "People really need to protect themselves."

Virus cases and deaths have hit record levels in the US, and television news reports show distraught nurses struggling to hold back tears as they labour in overwhelmed Covid wards.

The latest big public gathering came Saturday in Valdosta, Georgia, when President Trump held his first rally since the election, drawing thousands of people, packed tightly together and with few wearing masks.

The president has long minimised the severity of the pandemic, and at his rally barely mentioned the virus.

More than 2,500 people have died from Covid-19 each day for last five days in the United States - the highest numbers since the pandemic erupted.

But since his election loss on November 3 to Democrat Joe Biden, Trump has issued far more tweets challenging his defeat than addressing the virus.

Biden, who has said he will urge all Americans to wear masks for 100 days when he takes power in January, expressed doubt Friday about the administration's planning for the vaccine rollout.

"There is no detailed plan that we've seen, anyway, as to how you get the vaccine out of a container, into an injection syringe, into somebody's arm," he said.

Asked about that on Sunday, Azar dismissed it as "just nonsense," saying on Fox that the administration had been fully transparent.

But he declined to specifically criticize plans by Trump and other top officials to host big indoor holiday parties.

"Our advice remains the same in any context," he said, "which is wash your hands, watch your distance, wear face coverings when you can't watch your distance, and be careful of those indoor settings."