The official name for this inoculation gun is ‘PED-O-JET’. The inventor was Aaron Ismach.
“Developed in the 1960s, inoculation guns were used to vaccinate large numbers of people very quickly – up to a thousand people could be treated every hour. Instead of using a needle, the vaccine was forced through the skin at high pressures created using a foot pump.
However, the Ped-O-Jet was expensive and needed regular maintenance, which was not always available. Initially seen as a major weapon in the drive to eradicate smallpox globally, the guns were eventually replaced in favor of simple bifurcated needles.
Most mass inoculation guns of this type would later be withdrawn because of concerns about cross-infection. This example was made by Scientific Equipment Manufacturing Corporation.” – Description.
Ismach, Aaron. Hydraulic Multidose Inoculation Gun, 1975. Science Museum Group, under Creative Commons Attribution 4.0 license.