Between 1995 and 2014, pharmacists in the United States acquired new legal rights to provide vaccination services in retail pharmacies. The details of pharmacy vaccination regulations continue to vary across states with respect to disease types, patient characteristics, and physician supervision requirements. The consequences of pharmacy based immunization population health and social welfare are somewhat complicated. On the one hand, the retail pharmacy model may increase vaccination rates and reduce the prevalence of vaccine preventable diseases by making it easier and more convenient for people to be vaccinated. On the other hand, the retail model may have its largest effects among people who benefit the least from vaccination and some analysts worry that it may “unbundle”  and erode the package of preventive and diagnostic health services that are included in the conventional model of primary health care. In this paper, we document the evolution of pharmacy based vaccination regulations in the United States and describe the practical implications of common features of state regulations. We present evidence on the extent to which pharmacists have been trained or re-trained to safely administer vaccines. We estimate generalized difference in difference regressions to study the effects of the regulations along several dimensions.  We start by studying the effects of regulation on vaccination rates overall and in sub-populations with different opportunity costs of primary care visits and different expected benefits from vaccination. We go on to study the effects of the regulations on prevalence vaccine preventable diseases. Finally, we examine the unbundling effect by studying the effects of the regulations on consumption of primary care health services.