Needle injection is a skilled act. Jet injectors requires significantly less skill and training. This is useful for some models of mass vaccinations. Edit: Als

Needle injection is a skilled act. Jet injectors requires significantly less skill and training. This is useful for some models of mass vaccinations. Edit: Also just speculating, for this specific vaccine is looks like jet injection is actually preferred. The requirement to place the injection under the skin versus into the muscle seems like it has a tighter tolerances that would be more difficult to achieve with needle injection.