WILMINGTON, Del. — President-elect Joe Biden on Monday warned of dire consequences if President Trump and his administration continue to refuse to coordinate with his transition team on the coronavirus pandemic and block briefings on national security, policy issues and vaccine plans.

The remarks marked Biden’s toughest comments to date on Trump’s failure to acknowledge his election loss and cooperate with the incoming administration for a peaceful transfer of power.

“More people may die if we don’t coordinate,” Biden told reporters during a news conference in Wilmington, Delaware.

President-elect Joe Biden speaks about economic recovery at The Queen theater on Monday in Wilmington, Del. He said vaccine distribution is a “huge, huge undertaking,” and if his team has to wait until he takes office to dig into the distribution plan, they’ll be months behind. Andrew Harnik/Associated Press

Biden and his aides — and a small but growing group of Republicans — have emphasized the importance of being briefed on White House efforts to control the pandemic and distribute prospective vaccines. The Trump administration is working on its own distribution plan, while Biden’s chief of staff indicated his transition team will proceed with their own planning separately because of the obstruction.

Sen. Susan Collins, R-Maine, said it’s “absolutely crucial that the apparent president-elect and his team have full access to the planning that has gone on” for vaccine distribution.

“It is no easy matter” to distribute a vaccine, Collins said, so “it’s absolutely imperative for public health, that all of the planning that’s gone on for which the current administration deserves credit, be shared with the new administration.”

Collins’ remarks were echoed Monday by Republican Sen. Lisa Murkowski of Alaska. Last week, a larger group of Republicans in Congress called on the Trump administration to allow Biden to begin receiving national security briefings.

The outgoing president has refused so far to bend to pressure from Democrats or Republicans as he continues to dispute his loss to Biden, who has surpassed the 270 electoral vote threshold to become president and is leading Trump by more than 5.5 million votes nationally.

Cooperation between the outgoing and incoming administrations, traditionally a key component to the peaceful transfer of power in the United States, takes on heightened significance this year because of the coronavirus pandemic, which is escalating dramatically heading into the holiday season.

Biden called the vaccine distribution a “huge, huge undertaking,” and said that if his team has to wait until he takes office to dig into the government’s distribution plan, they’ll be “behind, over a month, month and a half.”

Before taking questions, Biden outlined his plans to alleviate inequality and boost the U.S. economy but said that any structural reforms depended first on reining in the pandemic and delivering more immediate relief.

“Once we shut down the virus and deliver economic relief to workers and businesses, then we can start to build back better than before,” he said.

President-elect Joe Biden and Vice President-elect Kamala Harris attend a briefing on the economy at The Queen theater. Before the address, they had virtual meetings with AFL-CIO President Richard Trumka, General Motors CEO Mary Barra and Microsoft CEO Satya Nadella. Andrew Harnik/Associated Press

Biden has vowed to spend trillions of dollars to reinvigorate U.S. manufacturing, expand health care coverage and combat climate change, among other priorities. But his chief priority remains controlling the pandemic, which is surging to record levels and forcing state and local leaders to implement new rounds of restrictions on local businesses.

The president-elect has so far tried to sidestep difficult questions about whether he might support a short-term national lockdown to arrest the surge of coronavirus cases. Since defeating Trump, Biden has devoted most of his public remarks to encouraging Americans to wear masks and embrace social distancing measures.

But members of his coronavirus advisory board have been more specific. One member, Michael Osterholm, recently suggested a four- to six-week national lockdown with financial aid for Americans whose livelihoods would be affected. He later walked back the remarks and was rebutted by two other members of the panel who said a widespread lockdown shouldn’t be under consideration.

Speaking Monday on “CBS This Morning,” Osterholm was not asked about a potential lockdown, but he said the nation needs “a standard set of principles.”

“Right now, we don’t have a standardized set so you’re hearing all these governors and mayors are scrambling to try to find what is the right answer for us, and it would surely help all of them, and that’s what I’m hearing from them, that we have a standardized set of recommendations and protocols,” he said.

Biden was asked Monday whether he would encourage leaders to look at potentially reinstating stay-at-home orders now that the pandemic is surging nationwide. He avoided answering directly and instead called on officials to embrace mask-wearing and criticized those who haven’t.

Before his Monday address, Biden and Vice President-elect Kamala Harris held virtual meetings with AFL-CIO President Richard Trumka, General Motors CEO Mary Barra and Microsoft CEO Satya Nadella, among others.

The U.S. economy has recovered from the pandemic-induced shutdowns this spring more quickly than most economists expected. The unemployment rate dropped a full percentage point last month to 6.9% and those who still have jobs — many of them working from home — have stepped up their spending on cars, electronics and home renovations.

But much of the rebound was fueled by $2 trillion in stimulus money that has largely run its course. And there are signs that the ongoing increases in confirmed virus cases are making Americans more cautious about traveling and shopping.

Consumers cut back on spending in early November, according to JPMorgan Chase, which tracks spending on 30 million of its debit and credit cards. Spending declines have been larger in some states with severe outbreaks, such as Iowa and North Dakota.

Most economists support another round of stimulus funding, including loans to small businesses, extended unemployment benefits and support for states and cities. Congressional Democrats have previously backed another $2 trillion in aid.

Sen. Mitch McConnell, the Republican majority leader, has pointed to the falling unemployment rate as evidence that much less stimulus is needed.

But on whether Biden should receive coronavirus briefings, many of Trump’s allies on Capitol Hill remained dug in.

“We’ve been working for the past year to make sure the vaccine will be delivered and it will be starting to be delivered probably in December, so he won’t even be president of the United States when the vaccine starts,” Sen. John Cornyn, R-Texas, said in pushing back against Biden’s comments.

“He can be privy, but he won’t have anything to do with it,” Cornyn said. “I mean, I hope by the time he’s inaugurated that we’re going to be well underway.”