Historically, multi-use nozzle jet injector (MUNJI) devices with reusable nozzles were used successfully worldwide in the latter half of the 20th century to deliver countless millions, or by some estimates billions of doses of vaccines to both adults and children over the course of several decades (Weniger and Papania 2008) . In response to the risks of disease transmission due to cross contamination from reuse of injection devices, a new generation of jet injector designs were developed starting in the late 1980s to address this safety concern. These new jet injectors utilize a sterile, disposable cartridge or syringe for each patient injection and a reusable hand-piece that relies on a power source, such as a manually powered spring or gas canister. A number of disposable-syringe jet injectors (DSJIs) have been developed and approved by national regulatory authorities for a variety of applications and uses, including vaccine delivery. Some of these are low-cost, manually powered DSJI technologies, developed specifically for application to developing countries' immunization requirements and needs, which include design features to prevent reuse ('auto-disable') of the needle-free syringes. DSJIs in clinical development for ID delivery include the Biojector Ò 2000 and Zetajet Ò (Bioject), and PharmaJet Ò (PharmaJet Inc.).