President-elect Joe Biden has grown frustrated with the team in charge of plotting his coronavirus response, amid rising concerns that his administration will fall short of its promise of 100 million vaccinations in the first 100 days, according to people familiar with the conversations.

Biden has expressed criticism on multiple occasions to groups of transition officials — including one confrontation where Biden conveyed to Covid coordinator Jeff Zients and his deputy, Natalie Quillian, that their team was underperforming…

Still, the U.S. has conducted around 7 million vaccinations over its first three weeks, well below the million-a-day rate Biden will need to hit. While some Biden advisers insist it’s possible to make good on the 100-million vow, others are privately worried that the federal response is already so chaotic that it will take a herculean effort to pull it off.

Transition officials described encountering a litany of challenges and a lack of long-term planning by the Trump administration, putting them in a hole so deep it could take weeks to get the vaccination campaign on track. They conceded that the team is still working to solve some of the most pressing issues.