A needle-free jet injection was a system widely deployed around 1967 for mass vaccinations. Devices like the U.S.-developed Ped-O-Jet used high-pressure liquid jets (fired at bullet-like speeds of up to 1,200 psi) to “penetrate the skin painlessly in a fraction of a second” without any physical needle.
Source: x.com/moscow_en
1960s Vaccine Injector — “Ped-O-Jet”
