Biden: 'Darkest days' of pandemic still ahead

US President-elect Joe Biden says that the worst is yet to come amid the coronavirus pandemic and called on Americans to remain vigilant over the holidays.

More than 320,000 COVID-19 deaths have been reported so far in the United States, the highest in the world.

Biden said in a news conference on Tuesday that it will take many more months to deliver vaccines to millions of US citizens.

Biden said, "our darkest days in the battle against COVID are ahead of us, not behind us." He said tens of thousands of more lives could be lost in the coming months.

On the economic relief package passed by Congress on Monday, Biden said the bill is just a first step -- "a down payment." He pledged to lay out additional relief measures, including more funds, when he takes office on January 20.

When asked about the new variant of the virus that appears to be spreading in the UK, Biden said he had asked his COVID task force whether testing should be required before people can board an aircraft to fly back to the United States. He said he had also asked the team whether those passengers should quarantine. Biden said he is waiting to hear from his experts.