Donald Trump and Joe Biden offered sharply contrasting reactions on Monday to news of a coronavirus vaccine that proved nearly 95% effective in trials. In a press conference the president-elect called the vaccine news “really encouraging” but warned “more people may die” unless the Trump administration starts cooperating with the incoming Democratic administration. “We are going into a very dark winter. Things are going to get much tougher before they get easier,” he said. Rather than working to combat the virus, which is spreading faster than ever and on average killing more than 1,000 Americans a day, Trump has stayed focused on unsubstantiated claims that the presidential election was stolen. Pharmaceutical giant Moderna said on Monday its experimental vaccine was 94.5% effective, based on interim data from a late-stage clinical trial. “Another vaccine just announced,” Trump tweeted, seeking to claim credit. “This time by Moderna, 95% effective. For those great ‘historians’, please remember that these great discoveries, which will end the China Plague, all took place on my watch!” Critics say Trump has all but surrendered to the pandemic, which has killed more than 244,000 people in the US and is averaging more than 100,000 cases per day. Michael Osterholm, an adviser to Biden, told NBC on Sunday: “We are in a very dangerous period – the most dangerous public health period since 1918.” Yet Trump has not attended a taskforce meeting in “at least five months”, public health expert Dr Anthony Fauci said on Sunday, and seems to have bet everything on a vaccine. Trump appeared consumed instead by the election – and now by denying its outcome. Biden beat him by the same 306-232 margin in the electoral college Trump described as a “landslide” when he won in 2016. The Democrat is also ahead in the popular vote by 5.5m votes, or 3.6%, with ballots still being counted. The Trump administration has not recognised Biden as president-elect, preventing his team from gaining access to government office space and funding. Democrats and some Republicans have warned that refusal to give Biden access to intelligence poses a risk to national security and hampers the battle against the virus, including vaccine distribution planning. Biden said the delay was “more embarrassing than debilitating” and that he was continuing to put in place his team and plans to deal with the pandemic and its economic fallout. The pandemic is the most pressing crisis facing the incoming president. Ron Klain, who will be White House chief of staff, said Biden advisers would meet Pfizer and other drugmakers this week. White House officials and Republicans in Congress are outnumbered by world leaders in acknowledging Biden’s win. On Monday Robert O’Brien, Trump’s national security adviser, noted that a transition would only take place “if the current lawsuits don’t work out for the president”. But speaking at the Global Security Forum, O’Brien acknowledged: “If there is a new administration, they deserve some time to come in and implement their policies. “We may have policy disagreements but look, if the Biden-Harris ticket is determined to be the winner – and obviously things look that way now – we’ll have a very professional transition from the National Security Council. There’s no question about it.” The president appeared on Sunday to publicly acknowledge that Biden had won the election, but then backtracked and reiterated his false claim the vote was rigged. Trump, who has put Rudy Giuliani, the former New York mayor, in charge of his legal offensive, tweeted on Sunday that he would soon file “big cases” challenging election results. However, his campaign has already lost numerous court battles and dropped a major part of a suit seeking to prevent Pennsylvania from certifying its results, narrowing the case to a small number of ballots. Biden won the state by more than 68,000 votes. On Monday Trump tweeted: “The Radical Left Democrats, working with their partner, the Fake News Media, are trying to STEAL this Election. We won’t let them!” In a statement issued last week by the lead US cybersecurity agency, federal election security officials dismissed such “unfounded claims” and expressed “utmost confidence” in the integrity of the elections. Officials from both parties have said there is no evidence of major irregularities. Biden has called Trump’s refusal to concede “an embarrassment” and is pressing ahead with the transition. On Monday afternoon he and running mate Kamala Harris were due to speak “on the economic recovery and building back better in the long term”, in their first speech addressing the economic situation since their victory. Biden outlined a $7.3tn plan ahead of the election that among other goals would bolster crumbling infrastructure, build a clean energy economy and support domestic manufacturing with cash for research and development. His first aim is to pass a new stimulus plan. But it is unclear how likely he is to pass any deal while Republicans control the Senate, which will hinge on runoff elections in Georgia in January. Talks about a new stimulus package have been deadlocked for months. The economic situation has improved but remains on a knife edge. Unemployment has dropped dramatically since a high of 14.7% in April but worrying signs remain. By October the unemployment rate had fallen to 6.9% but the number of long-term unemployed – those jobless for 27 weeks or more – increased by 1.2 million to 3.6 million. Almost a third of the total number of people out of work are now long-term unemployed, black and latino Americans suffering far higher rates of unemployment than their white neighbors. Jobs growth has continued to slow and each week people are filing unemployment claims at a rate still more than three times as high as before the pandemic. Elise Gould, senior economist at the Economics Policy Institute, said: “If this drags on and the pace of jobs growth continues to slow, it will take years before we get back to a pre-pandemic economy. Americans can not afford the political games that are being played.”