We’ve taken the people with the least amount of resources and capacity and asked them to do the hardest part of the vaccination — which is actually getting the vaccines administered into people’s arms,” said Dr. Ashish Jha, the dean of Brown University’s School of Public Health.Coronavirus Briefing: An informed guide to the global outbreak, with the latest developments and expert advice.Sign UpFederal and state officials have denied they are to blame for the slow rollout. Officials behind Operation Warp Speed, the federal effort to fast-track vaccines, have said that their job was to ensure that vaccines are made available and get shipped out to the states. President Trump said in a tweet on Tuesday that it was “up to the States to distribute the vaccines once brought to the designated areas by the Federal Government.”“Ultimately, the buck seems to stop with no one,” Dr. Jha said.These problems are especially worrisome now that a new, more contagious variant, first spotted in Britain and overwhelming hospitals there, has arrived in the United States. Officials in two states, Colorado and California, say they have discovered cases of the new variant, and none of the patients had recently traveled, suggesting the variant is already spreading in American communities.The $900 billion relief package that Mr. Trump signed into law on Sunday will bring some relief to struggling state and local health departments. The bill sets aside more than $8 billion for vaccine distribution, on top of the $340 million that the C.D.C. sent out to the states in installments in September and earlier in December.