If you look at the actual study Chart B, the differences in vaccine hesitancy depending on levels of education seem to be split into two intertwined clusters: High School or Less, Some College, and PhD in one group, and Four-Year College Degree, Master's, and Professional Degree in the other, with the first group about twice as hesitant as the second. The term "Professional Degree" includes medical professionals (doctors, nurses, dentists, veterinarians, and the like), lawyers, and licensed engineers.
A more stark division can be seen in Chart D, which shows the vaccine hesitance rate divided according to the proportion of t support in the last election in the county in which the respondents lived. To put it simply, the higher the local t support, the freedumber they are.