Jet injector

A health worker using a jet injector on a child

A jet injector is a type of medical injecting syringe that uses a high-pressure narrow jet of the injection liquid instead of a hypodermic needle to penetrate the epidermis. It is powered by compressed air or gas, either by a pressure hose from a large cylinder, or from a built-in gas cartridge, small cylinder, or spring (as in the MadaJet, Medijector Vision, Vitajet, Injex 23 and 30, or Insujet).

Jet injectors are used for mass vaccination, and as an alternative to needle syringes for diabetics to inject insulin. As well as health uses, similar devices are used in other industries to inject grease or other fluid.

The term "hypospray" is largely restricted to science-fiction, but there are cases in scientific periodicals of a real jet injector being called a hypospray.[1][2][3]


A Med-E-Jet vaccination gun from 1980

A jet injector, also commonly referred to as an air gun, air jet injector, pneumatic injector, or jet gun injector, is a needle-free instrument that uses a high-pressure stream of liquid medicament to penetrate the skin and achieve a percutaneous administration of medicine or vaccine. The concept most resembles a powerful squirt gun penetrating through skin.

Initially jet injectors were developed as an easier method for delivering insulin to diabetic children who had a fear of needles. Soon thereafter developers designed a type of jet injector which reused the same nozzle tip to vaccinate multiple people. These jet injectors, known as high workload jet injectors, were designed for use in mass immunizations, in which a large population needed to be vaccinated at a rapid rate. The concept reduced the overuse and disposal of single-use syringes and needles, and prevented the accidental needle stick injuries to the immunizing staff.


Jet injectors are defined in law under Title 21 of the Code of Federal Regulation. These devices are listed under sections for General Hospital and Personal Use Devices and Dental Instruments.

Nonelectrically powered jet injectors are defined in section 880.5430 as a “nonelectrically powered device used by a health care provider to give a hypodermic injection by means of a narrow, high velocity jet of fluid which can penetrate the surface of the skin and deliver the fluid to the body.”

Other types of jet injectors have been defined by their design features. Gas-powered jet injectors are defined in section 872.4465 as a “syringe device intended to administer a local anesthetic. The syringe is powered by a cartridge containing pressurized carbon dioxide which provides the pressure to force the anesthetic out of the syringe.”

Spring-powered jet injectors are defined in section 872.4475 as a “syringe device intended to administer a local anesthetic. The syringe is powered by a spring mechanism which provides the pressure to force the anesthetic out of the syringe.”


These devices can be divided into various classes or categories based upon different factors. Factors such as:

1. Intended Market—Is the intended population human or animal? Medical professionals have used jet injectors for administering vaccines, therapeutic drugs, anesthetics, antibiotics, anticoagulants, antivirals, corticosteroids, cytotoxics, immunomodulators, insulin, hormones, and vitamins.[4] Veterinarians have used jet injectors to deliver vaccinations to various animals, but mainly livestock.

2. Intended Usage—Devices can be used by health professionals for vaccinating multiple patients or can be used solely for self-administration whereupon one patient uses one device.[5] The largest market for self-administering jet injectors is for administering insulin.

3. Frequency of vaccinations—High Workload versus Low Workload Jet injectors. High workload jet injectors are devices which can inject more than 150 people per hour. These devices are designed for use in mass immunization campaigns, in which a large number of people need to be vaccinated at a rapid rate. Low workload jet injectors are devices which can inject on average 30 people per hour. These devices are intended for use in physicians’ offices.[6]

4. Design of the Drug Compartment—The drug compartment has been redesigned over the years to overcome the inherent risk of cross-contamination via the nozzle and internal fluid pathways. These design changes can be best classified by using the term “generation.” Below are descriptions of first generation, second generation and third generation jet injectors whereupon each succeeding generation has been an improvement to the faults of the previous generation.

First Generation Jet Injectors consisted of reusable nozzles and internal fluid pathways. None of these devices had any disposable parts. Parts that became contaminated with blood had to be substituted until contaminated parts could be sterilized through autoclaving, a procedure that sterilized devices through steam and high-temperature within an enclosed container. These first generation devices were termed multi-use nozzle jet injectors or MUNJI. In more recent years, researchers termed MUNJIs as reusable-nozzle jet injector, which describe the same device. Reusable-nozzle jet injectors are defined as a “Needle-free jet injector for high-speed vaccination which feeds vaccine from multidose vials through reusable fluid chambers, pathways, and nozzles that are in contact with consecutive patients without intervening sterilization”.[7] These devices were found to act as vehicles allowing blood and disease to pass from one patient to the consecutive patient.

Second Generation Jet Injectors attempted to overcome this risk by implementing a single-use protector cap that covered the injector nozzle thus acting as a shield between the reusable nozzle and the patient’s skin. Following an injection the protector cap would be discarded and a new one put in its place. These second generation devices were termed protector cap needle-free injectors or PCNFI.

Kelly and colleagues (2008)[8] found in their study that PCNFIs still allowed cross-contamination of the hepatitis B virus through contaminating the internal fluid pathway. Researchers learned to overcome the risk of cross-contamination that the internal fluid pathway and patient-contacting parts cannot be reused.

Third Generation Jet Injectors completely overhauled the design of preexisting devices, by making the drug compartment, internal fluid pathway, and nozzle as a single-use disposable cartridge. Once this cartridge dispenses an injection it can no longer be reused and must be discarded. Depending upon the manufacturer the cartridge may also be referred to as an “ampoule,” “syringe,” “capsule,” or “disc”.[9] These third generation devices were termed disposable-cartridge jet injectors or DCJI. So far, this design has overcome the risk of cross-contamination although further tests are needed.

Modern Jet Injector Brands

The Biojector 2000 is a make of gas-cartridge-powered jet injector. It is claimed by its manufacturer that it can deliver intramuscular injections and subcutaneous injections up to 1 milliliter. The part which touches the patient's skin is single-use and can be replaced easily. It can be powered from a big compressed gas cylinder instead of gas cartridges. It is made by Bioject.[10]

The Vision (MJ7) is a compact, spring-powered jet injector. It can deliver up to 1.6ml in 0.03ml increments, and is designed to last 3000 injections. The medication travels through a hole in the needle-free syringe that is about half the diameter of a 30 gauge syringe. The part which touches the patient's skin can be used for a week. The device was designed by Antares Pharma (formerly Medi-Jector).[11]

The PharmaJet Needle-Free Injector delivers vaccines either intramuscularly or subcutaneously by means of a narrow, precise fluid stream syringe that delivers the medicine or vaccine through the skin in one-tenth of a second.[12]

Diabetics have been using jet injectors in the United States for at least 20 years. These devices have all been spring loaded. At their peak, jet injectors accounted for only 7% of the injector market. Currently, the only model available in the United States is the Injex 23. In the United Kingdom, the Insujet has recently entered the market. As of June 2015, the Insujet is available in the U.K. and a few select countries.


Since the jet injector breaks the barrier of the skin, there is a risk that blood and biological material is transferred from one user to the next. Research on the risks of cross-contamination arose immediately after the invention of jet injection technology. The website Jet Infectors has documented the risks and hazards of jet injectors.

There are three types of inherent problems with jet injectors:

1. Splash-Back

Research conducted by Samir Mitragotri, a chemical engineer at the University of California, visually captured the discharge of multiple-use nozzle jet injectors using high-speed microcinematography.[13] The photos in the following link demonstrate a close-up look at the jet injection process. Most importantly, notice in the images when the high velocity stream penetrates the skin there is extensive splash back.

“The black region at the top of each image shows the outline of a jet injector with the protrusion in the centre showing the position of the nozzle,” said Mitragotri. “The black region at the bottom shows the outline of human skin.” The white space between the two black regions is a gap, approximately a few millimeters wide between the jet injector and human skin.

From 280 μs to 1 ms (i.e., Millisecond) the penetration of the jet stream caused excessive splash back. Mitragotri stated, “The typical volume of the liquid splashed in the image at 400 μs is around 100 nl [i.e., Nanoliter].

Mitragotri’s photographic evidence leaves no dispute, during the natural injection process that was intended by the manufacturer, the nozzle frequently became contaminated. Thus, the jet injector became unsterile and therefore unsafe.

Hoffman and colleagues (2001)[14] also observed the nozzle and internal fluid pathway of the jet injector became contaminated. Epidemiologist, Dr. Peter Hoffman, termed this phenomena as ballistic contamination in a 1999 JAMA article.[15] With the jet injector being directly behind the site of impact it is a prime target to becoming contaminated as evidenced in Mitragotri’s photographs.

2. Fluid Suck-Back

Aaron Ismach, inventor of the most widely used jet injector, the Ped-O-Jet, found earlier devices sucked fluid directly upon the outside of the nozzle orifice back into internal fluid pathway and drug reservoir. This phenomenon allows foreign particles to contaminate the sterile vaccine. Ismach declared in his 1962 patent that his invention overcame this danger. “Unlike most earlier hypodermic jet injection guns,” writes Ismach. “The instant invention [the Ped-O-Jet] is free from danger of sucking fluid back from a patient either during or after the firing cycle is completed so that the danger of cross-infection is almost completely avoided”.[16]

Despite Ismach’s assertions, investigations conducted by the CDC found otherwise. Dr. Bruce Weniger, former Lead Researcher on Vaccine Technology within the CDC and leading expert on jet injection technology, recalled the CDC’s 1980s investigation into jet injectors. Dr. Weniger wrote, “After injections, they [CDC] observed fluid remaining on the Ped-O-Jet nozzle being sucked back into the device upon its cocking and refilling for the next injection (beyond the reach of alcohol swabbing or acetone swabbing)”.[17]

3. Retrograde Flow

Kale and Momin (2014)[18] found during Phase 2 of the injection process there would be a backwards flow where the jet spray would shoot back-out of the hole towards the jet injector. This would be an expected phenomena in every injection due to the continuous depletion of pressure where the volumetric rate of hole formation would eventually be less than the volumetric rate of the jet impinging the skin. This continuous decrease in pressure would create a retrograde, or rather backwards flow, whereupon the jet injector’s nozzle, internal fluid pathway and drug reservoir would become contaminated.

Suria and colleagues (1999)[19] found retrograde flow, as well:

“firing the jet injector onto a contaminated surface (gauze pad contaminated with 4 cm3 of 108 CFU/mL S aureus) caused back flow of bacteria into the internal canal, as indicated by growth of bacteria after firing of sterile liquid through the contaminated device onto agar plates. The degree of back flow and resulting contamination increased with increasing ejection volume setting, from lowest (0.06 cm3) to highest (0.30 cm3).”

Hoffman and colleagues (2001) found retrograde flow:

“some of the liquid injected form[ed] a pocket below the injection site. This will be under maximum pressure towards the end of the injection process, before sufficient dispersion into surrounding tissues has occurred to release pressure. This will coincide with a lessening of pressure from the injector. When the pressure from the injector is exceeded by the back-pressure from the tissue pocket, backflow through the pathway in the skin created by the injector could occur. This liquid will contain blood from the destruction of small blood vessels during the injection process and can have different pathways after it has emerged from the skin according to the type of injector. Injectors that have direct skin contact will form a continuous fluid pathway between the skin and injector. As the outward pressure from the injector dies away at the end of an injection, back-pressure from the fluid in the tissue pocket will cause blackflow out of the skin to inside the injector’s fluid pathway.”

The Programme for Appropriate Technology in Health (PATH) has worked to develop jet injection technology over the past twenty-years. PATH ran parallel tests to Hoffman’s preliminary study. The in-vitro tests of the Ped-O-Jet (later renamed Am-O-Jet) confirmed similar findings. PATH found “a correlation between the extent of contamination and the level of back-pressure in simulated skin models”.[20]

Kelly and colleagues (2008) tested the potential cross-contamination of the Hepatitis B Virus via a new protector cap needle-free injector. The invention attempted to overcome the risk of cross-contamination by implementing a single-use protector cap that covered the injector nozzle thus acting as a shield between the reusable nozzle and the patient’s skin. Following an injection the protector cap would be discarded and a new one put in its place. However, Kelly and colleagues found cross-contamination of the Hepatitis B Virus occurred without any visible bleeding at the injection site. In 7 out of the 17 injections that tested positive for cross-contamination researchers observed no visible bleeding at the injection site. This indicated that cross-contamination of blood-borne viruses successfully occurred within microscopic levels of blood not visible to the human eye. The study also demonstrated retrograde flow allowed blood-borne pathogens to permeate the single-use protector cap and enter the jet injectors internal fluid pathway.

Hepatitis B can be transmitted by less than one millionth of a millilitre[21] so makers of injectors need to ensure there is no cross-contamination between applications. The World Health Organization no longer recommends jet injectors for vaccination due to risks of disease transmission.[22]

Numerous studies have found cross-contamination of diseases from jet injections. An experiment using mice, published in 1985, showed that jet injectors would frequently transmit the viral infection LDV from one mouse to another.[23] Another study used the device on a calf, then tested the fluid remaining in the injector for blood. Every injector they tested had detectable blood in a quantity sufficient to pass on a virus such as hepatitis B.[21]

From 1984–1985 a weight-loss clinic in Brazil injected a pregnancy hormone into their clients, mostly using a jet injector. It was noted that a number of these patients became sick with hepatitis. When studied, 57 out of 239 people who had received the jet injection tested positive for hepatitis B.[24]

As well as transmission between patients, jet injectors have inoculated bacteria from the environment into users. In 1988 a podiatry clinic used a jet injector to deliver local anaesthetic into patients' toes. Eight of these patients developed infections caused by Mycobacterium chelonae. The injector was stored in a container of water and disinfectant between use, but the organism grew in the container.[25] This species of bacteria is sometimes found in tap water, and had been previously associated with infections from jet injectors.[26]


Accidental jet injection

Accidents have happened in vehicle repair garages and elsewhere where one of the following has unintentionally acted as a hypodermic jet injector:

Accidental injection of oil or paint by such high-pressure sprays can cause very serious injuries which may require amputation, and can induce fatal sepsis.


  1. Clarke AK, Woodland J (February 1975). "Comparison of two steroid preparations used to treat tennis elbow, using the hypospray". Rheumatol Rehabil. 14 (1): 47–9. doi:10.1093/rheumatology/14.1.47. PMID 1091959.
  2. Hughes GR (June 1969). "The use of the hypospray in the treatment of minor orthopaedic conditions". Proc. R. Soc. Med. 62 (6): 577. PMC 1811070Freely accessible. PMID 5802730.
  3. Baum J, Ziff M (March 1967). "Use of the hypospray jet injector for intra-articular injection". Ann. Rheum. Dis. 26 (2): 143–5. doi:10.1136/ard.26.2.143. PMC 1031030Freely accessible. PMID 6023696.
  4. Weniger, Bruce; Papania, Mark. "Alternative Vaccine Delivery Methods" (PDF). Retrieved October 23, 2016.
  5. Weniger, Bruce; Papania, Mark. "Alternative Vaccine Deliver Methods" (PDF).
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  12. "PharmaJet Product Page".
  13. Mitragotri, Samir (2006 July). "Current status and future prospects of needle-free liquid jet injectors". Nat Rev Drug Discov. 5 (7): 543–8. PMID 16816837. Check date values in: |date= (help)
  14. Hoffman, Peter; Abuknesha, RA; Andrews, NJ; Samuel, D; Lloyd, JS (2001). "A model to assess the infection potential of jet injectors used in mass immunization". Vaccine. 16 (19): 4020–7. PMID 11427278.
  15. Voelker, Rebecca (May 26, 1999). "Eradication Efforts Need Needle-Free Delivery". JAMA. 281 (20). Retrieved October 23, 2016.
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  20. World Health Organization. "STEERING GROUP ON THE DEVELOPMENT OF JET INJECTION FOR IMMUNIZATION" (PDF). Retrieved October 23, 2016.
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  22. World Health Organization (2005-07-13). "Solutions: Choosing Technologies for Safe Injections". Archived from the original on 21 September 2012. Retrieved 2011-05-06.
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  24. Canter, Jeffrey; Katherine Mackey; Loraine S. Good; Ronald R. Roberto; James Chin; Walter W. Bond; Miriam J. Alter; John M. Horan (1990-09-01). "An Outbreak of Hepatitis B Associated With Jet Injections in a Weight Reduction Clinic". Arch Intern Med. 150 (9): 1923–1927. doi:10.1001/archinte.1990.00390200105020. PMID 2393323. Retrieved 2011-05-06.
  25. Wenger, Jay D.; John S. Spika; Ronald W. Smithwick; Vickie Pryor; David W. Dodson; G. Alexander Carden; Karl C. Klontz (1990-07-18). "Outbreak of Mycobacterium chelonae Infection Associated With Use of Jet Injectors". JAMA. 264 (3): 373–6. doi:10.1001/jama.1990.03450030097040. PMID 2362334.
  26. Inman, P.M.; Beck, A.; Brown, A.E.; Stanford, J.L. (August 1969). "Outbreak of injection abscesses due to Mycobacterium abscessus". Archives of Dermatology. 100 (2): 141–7. doi:10.1001/archderm.100.2.141. PMID 5797954.
  27. Rees CE (11 September 1937). "Penetration of tissue by fuel oil under high pressure from diesel engine". JAMA. 109 (11): 866–7. doi:10.1001/jama.1937.92780370004012c.
  28. The DoD order
  29. Veterans info page
  30. "PharmaJet's Stratis® Needle-free Injector Receives WHO PQS Certification as a Pre-qualified Delivery Device for Vaccine Administration". FierceVaccines.

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