US President-elect Joe Biden has named the members of his coronavirus task force, highlighting his pledge to make tackling Covid-19 his top priority.
Mr Biden said one of his "most important battles" was to manage the surge in cases and bring a safe and viable vaccine to the people.
He is also forging ahead on transition issues from climate change to migrants.
But President Trump still refuses to concede and is backing legal challenges to results in several key states.
Mr Biden's victory was declared on Saturday but it remains a projection, with a number of states still counting votes. The nationwide difference in votes for the two candidates is about 4.5 million.
Mr Biden and Vice-President-elect Kamala Harris have launched a website for the transition, saying the team will also focus on the economy and tackling racism.
But the president-elect will need the help of an agency called the General Services Administration to begin the transition process and its Trump-appointed head has given no indication when that will happen,
What are the Covid plans?
On Monday, Mr Biden set out the blueprints for his Transition Covid-19 Advisory Board.
In his first appointments since his victory was announced, he named three co-chairs and 10 members. Among the co-chairs named is Vivek Murthy, who was appointed US surgeon-general by President Barack Obama in 2014 and removed by President Trump in 2017.
One member is immunologist Rick Bright, who says he was ignored and then removed by the Trump administration over his early warnings on Covid.
In a statement, Mr Biden said the board would help to get the virus under control, deliver relief for working families, address racial disparities and work to reopen schools and businesses.
He also said it would "elevate the voices of scientists and public health experts". President Trump's comments on Covid-19 have often conflicted with scientists, including leading infectious disease expert Anthony Fauci.
Mr Biden on Monday also welcomed the news from Pfizer and BioNTech that preliminary analysis showed their vaccine in development could prevent more than 90% of people from getting Covid-19.
He thanked the "brilliant women and men who helped produce this breakthrough and to give us such cause for hope" but also warned it was "important to understand that the end of the battle against Covid-19 is still months away".
The focus of his policy will be on mask wearing, social distancing, contact tracing and hand washing.
Covid cases in the US since the epidemic began are nearing 10 million, and there have been more than 237,000 deaths recorded so far, Johns Hopkins research shows.
Donald Trump also welcomed the vaccine statement, tweeting that it was "such great news".
What are the other transition plans?
They reportedly include a slew of executive orders - written orders issued by the president to the federal government that do not require congressional approval - aimed at reversing controversial Trump policies. They are in draft form and cannot be issued until he takes office. According to US media:
- Mr Biden will rejoin the Paris climate agreement, which the US officially left on Wednesday
- He will reverse the decision to withdraw from the World Health Organization
- He will end the travel ban on citizens from seven mostly Muslim countries
- He will reinstate an Obama-era policy of granting immigration status to undocumented migrants who entered the US as children
Mr Biden also aims to make addressing racism a key policy, including better access to affordable housing for black and minority communities.
Mr Biden wants to transform US policing, including banning the use of chokeholds, and to reduce the US prison population, which at more than two million people is the biggest in the world.
However, for the transition process to begin, the support of the General Services Administration is needed to access government funds and communicate with the federal agencies it will be staffing.
Its administrator, Emily Murphy, has not started the process nor indicated when she will do so, sparking concern among some Democrats that Mr Trump will try to impede the transition process.
What have Mr Trump and Republicans said?
The vast majority of the president's tweets have continued to call the electoral process into question.
Mr Trump, the first president to lose a re-election bid since 1992, has launched an array of lawsuits backing claims of fraud for which no evidence has yet been presented.
One of his lawyers, Rudy Giuliani, on Monday said there were "unlawful votes" in Pennsylvania, Michigan, Georgia, Wisconsin and Nevada. "We will prove it all," he said.
Mr Trump still plans rallies to back his challenge, campaign spokesman Tim Murtaugh said.
Most Republicans have remained silent on Mr Biden's projected election victory, favouring the unveiling of full results.
The Republican leader in the House of Representatives, Kevin McCarthy, told Fox News that all recounts and legal challenges should be completed.
The New York Times said advisers had told Mr Trump the chances of legal success were not high but that he was not yet ready to accept the loss.
Mr Trump has vowed to take legal action as far as the Supreme Court.
If the election result is challenged, it would require legal teams to argue this in state courts. State judges would then need to uphold the challenge and order a recount, and Supreme Court justices could then be asked to overturn a ruling.
Former President George W Bush was one Republican who did congratulate Mr Biden, calling him a "good man".
What happens next?
Votes in some states continue to be counted and results are never official until final certification, which occurs in each state in the weeks following the election.
This must be done before 538 chosen officials (electors) from the Electoral College - which officially decides who wins the election - meet in their state capitals to vote on 14 December.
The electors' votes usually mirror the popular vote in each state. However, in some states this is not a formal requirement.
The new president is officially sworn into office on 20 January after a transition period to give them time to appoint cabinet ministers and make plans.
The handover of power takes place at a ceremony known as the inauguration, which is held on the steps of the Capitol building in Washington DC.
