In the past the military and public health officials used a jet injector with a hypodermic needle to vaccinate recruits and people during epidemics.
Disadvantages of the needle jet injector:
(1) trauma at the injection site, with bruising and pain
(2) possible transmission of viral infections
Needle-free injectors use a high-pressured jet of inert gas to drive the vaccine into the dermis and subcutaneous tissue of the patient.
However, viral hepatitis B has reportedly been transmitted by these devices. This is due to retrograde contamination of the nozzle head by body fluids released from a patient by the pressure wave. Viral hepatitis B is highly contagious and can be transmitted by minute amounts of blood. In theory other pathogens could be transmitted but this would be less likely.
Risk factors for disease transmission with a needle-free jet injector:
(1) failure to comply with administration instructions
(2) failure to clean the device properly
(3) failure to use an injection nozzle that minimizes retrograde contamination with body fluids
