NEW YORK:U.S. coronavirus cases crossed the 15 million mark on Tuesday as regulators moved a step closer to approving a COVID-19 vaccine and Britain started inoculating people, offering hope of slowing a pandemic that killed 15,000 Americans in the last week alone.

Record cases in at least three states - Arizona, Alabama and Ohio - pushed the cumulative case load to over 15 million, according to a Reuters tally of state and county data. With the virus showing no sign of abating, leading health officials are once again sounding the alarm of further spread when people gather for the year-end holidays.

"We’re in for a very challenging period," top infectious disease expert Dr. Anthony Fauci told a virtual summit on Tuesday.

In a bit of welcome news, Pfizer Inc cleared another hurdle on Tuesday when the U.S. Food and Drug Administration released documents that raised no new red flags over the safety or efficacy of the vaccine it developed with Germany's BioNTech SE.

The documents were prepared ahead of a meeting of a panel of outside advisers on Thursday to discuss whether to recommend FDA emergency use authorization (EUA) of the Pfizer vaccine. That could eventually provide relief to hospitals buckling under a record 101,498 COVID-19 patients as of Monday, up 16% in a week. Healthcare workers are expected to be among the first to receive the vaccine it if receives an EUA.

Health officials predict a swift green light enabling the United States to join Britain, which became the first Western nation to begin mass inoculations with the Pfizer vaccine on Tuesday.

The FDA advisory panel is expected to review Moderna Inc's COVID-19 vaccine next week, potentially giving the public two vaccines that could be distributed in coming weeks.

While China and Russia have moved forward with their own vaccines, Briton Margaret Keenan, 90, became the first person to receive the Pfizer vaccine outside of clinical trials when she received a shot at her local hospital in Coventry in central England.

The United States badly needs a new tool to fight a virus spinning out of control. Another 203,474 infections were reported on Monday and 1,582 people died.

HOLIDAY SURGES

In Arizona, one of 14 states without a mask mandate, health officials on Tuesday reported over 12,000 new coronavirus cases, eclipsing the previous record of 6,799 on Dec. 5.

Alabama, which together with Arizona is among about half of U.S. states that have not enacted new restrictions during the latest virus surge, also notched a record high number of cases on Tuesday, and so too did Ohio, according to a Reuters analysis.

Experts and officials have expected a surge in cases, hospitalizations and deaths in the aftermath of the Thanksgiving holiday when many Americans traveled to be with family and friends.

In an effort to curb rapidly growing virus metrics, North Carolina became the latest state to clamp down on businesses and social activities. Governor Ray Cooper on Tuesday introduced an order effective Friday that will require residents to stay home between 10 p.m. and 5 a.m., and businesses including restaurants, bars and most retail stores to close by 10 p.m.

"A month ago, we were deeply concerned to see daily case counts go above 3,000. Now, we’re shocked that the number has doubled, with some daily counts at more than 6,000," Cooper wrote on Twitter.

In California, most of the population is under heavy new restrictions and in Washington state, Governor Jay Inslee extended for three weeks a package of restrictions, including limits on gatherings and a ban on indoor dining.

Twenty-six states have recently enacted statewide measures to curb the spread of the virus.

President Donald Trump, who will be succeeded by President-elect Joe Biden on Jan. 20, has downplayed public health measures such as mask-wearing and social distancing to halt the virus spread, focusing instead on vaccine development.

Trump was to sign an executive order on Tuesday intended to ensure that priority access for COVID-19 vaccines procured by the U.S. government is given to the American people before assisting other nations.

Dr. Moncef Slaoui, a leader of the administration's Operation Warp Speed vaccine development program, said on Tuesday he was confident there will be enough vaccines to immunize 70% to 80% of the U.S. population by mid-May.

But Slaoui, speaking in an interview with Fox News, said he was more worried about the number of Americans who reject medical science and fear vaccines are unsafe or a conspiracy to harm the public than he was about supply issues.

"The highest concern I have is the level of hesitancy within the population as to accepting whether they will be immunized or not," Slaoui said, pleading with people to keep an open mind. "Please don't come to a conclusion before you have been exposed to the data."