Almost three weeks after the Food and Drug Administration authorized the shots, no one appears to be able to explain why immunizations are lagging. Some states are thought to be intentionally holding back shots, while others say it takes time to inoculate populations like the homebound.

Over the course of the last two weeks, senior Biden administration officials have met privately to try and determine what happened. Two senior administration officials believe states are conserving their J&J supplies until there’s enough to reach underserved communities and specific groups, like teachers or the disabled. But multiple state officials say they’re using whatever they get as soon as they get it.

What is clear is that around 2.3 million of the 4.3 million doses of the vaccine delivered have actually been administered. Between 140,000 and 200,000 doses have made it into people’s arms in recent days, according to the Centers for Disease Control.