Arizona's abrupt switch to an age-based COVID-19 vaccine rollout this week means some people 55 and older can get vaccinated, but that change is not consistent statewide. The new model is a hybrid. While the state is now emphasizing age-based vaccination, counties have the job of prioritizing the vaccination of front-line essential workers and vulnerable communities as they see fit. It's a simpler process, with the switch influenced by the decision that an age-based approach more quickly reaches the most people at higher risk. An age-based approach also eliminates figuring out how people would have to document their underlying health conditions to qualify.