“It had to go this way,” Paul Offit, a professor of pediatrics at Children’s Hospital of Philadelphia, told STAT. “We had to trip and fall and stumble and figure this out.”

Claire Hannan, executive director of the Association of Immunization Managers, said some of the gap between doses administered and delivered is likely due to a program run by CVS and Walgreens to vaccinate those in nursing homes. States participating in the program have to set aside 50% of their doses, which Hannan said could account for a share of the difference between doses shipped and doses administered nationally.

“I don’t think it’s bad,” she said of the pace of distribution so far. “I think it was always going to be like this. And I think that this is actually the easy part.”

The logistics of the rollout have been largely left up to states to navigate. States and local public health officials have warned for months that they would need more than $8 billion in additional funding to stand up the infrastructure needed to administer vaccines. The Trump administration instead provided states $340 million in funding to prepare for vaccinations. Congressional lawmakers also balked for months at appropriating additional funding for vaccine distribution, although the coronavirus stimulus package signed by President Trump on Sunday included $8 billion in funding for that effort.