Every year, a lack of vaccination leads to about 1.5 million preventable deaths, primarily in developing nations. One factor that makes vaccination campaigns in those nations more difficult is that there is little infrastructure for storing medical records, so there’s often no easy way to determine who needs a particular vaccine. MIT researchers have now developed a novel way to record a patient’s vaccination history: storing the data in a pattern of dye, invisible to the naked eye, that is delivered under the skin at the same time as the vaccine. “In areas where paper vaccination cards are often lost...