The vaccination levels for each state below are based on taking the total number of COVID-19 doses administered to date according to the Centers for Disease Control), then and dividing that into double the state population (since each person needs two doses to be fully vaccinated) as of April 2020 according to the U.S. Census Bureau.
I then adjust each state by counting the single-dose Johnson & Johnson vaccine twice (since it's effectively similar to getting 2 Pfizer or Moderna doses).
UPDATE 5/21/21: The first few times I did this, I estimated J&J at 3.5% for every state; since then I've found that the CDC does provide the exact number of each type of vaccine for every state...it ranges from as low as 1.9% in Hawaii to as high as 6.5% in Maine, which is kind of interesting. The later graphs at the bottom have been adjusted to reflect this.
But more than two in five Republicans said they would avoid getting vaccinated if possible, suggesting that President Biden has not succeeded in his effort to depoliticize the vaccines — and leaving open the question of whether the country will be able to achieve herd immunity without a stronger push from Republican leaders to bring their voters on board.