David Ridley, HSM Faculty Director, with co-authors Eli Liebman and Xiaoshu Bei, examined the drivers of vaccine shortages. In 2004 an Institute of Medicine report warned of vaccine shortages, raising concerns about disease outbreaks. More than a decade later, Ridley and his colleagues looked for progress in reducing vaccine shortages. They analyzed data on vaccine sales and shortages reported by practitioners and patients to the Food and Drug Administration and the American Society of Health-System Pharmacists in the period 2004–13. They found that the number of annual vaccine shortages peaked in 2007, when there were shortages of seven vaccines; there were only two shortages in 2013. There were no shortages of vaccines with a mean price per dose greater than $75 during the study period. Furthermore, they found that a 10% increase in price was associated with a nearly 1% decrease in the probability of a shortage. Government payers should carefully consider the benefits of averting shortages when evaluating prices for vaccines, including older vaccines whose prices have been subject to congressional price caps.