The jet injector is a needle-free injection device that uses a high-pressure stream to penetrate the skin and deliver medication into intradermal, subcutaneous, or intramuscular tissues. Multi-dose jet injectors are a type of jet injector with a reusable fluid path that consists of the vial adapter, dose chamber, fluid pathway, and nozzle. Although credited with decades of use and the delivery of millions of doses of vaccine in the field, multi-dose jet injectors are no longer used due to evidence of cross-contamination between injections. The HSI-500 Jet Injector with Protector Cap has been designed with a disposable plastic cap that acts as a shield between the nozzle and the skin to eliminate cross-contamination between injections while maintaining a high rate of vaccine delivery to multiple patients.