They've also provided quite a number of single doses. The numbers overall in the U.S. are 46% single dose and 34% two doses, but in the high-performing states, it's more like 60% and 45%. The reason you could do it was the vaccine supply. There was enough vaccine available from the two mRNA vaccines, less so the J & J vaccines. That was what made it possible: the procurement of vaccines at that scale.
On May 10th, 2021. See this statement in context.