Faulty Design Created Inherent Risks – Fluid Suck-Back

Fluid suck-back refers to any fluid or blood upon the nozzle being sucked into the orifice of the jet gun injector and contaminating the drug reservoir which holds the next dosage to be fired. Fluid suck-back occurs after the injection has been administered.

This undesirable phenomenon is likely due to a combination of the unit being pressurized and a faulty ball check-valve which created a vacuum at the end of the injection.


The following illustrations demonstrate this phenomenon.

Jet Infectors - Fluid Suck-back 1Jet Infectors - Fluid Suck-back 2Jet Infectors - Fluid Suck-back 3


And where is the evidence?


© Jet Infectors, 2016 – 2018

Research Documented Fluid Suck-back

During the mid- to late-1950s, researchers within the Department of Defense (DoD) became cognizant of the undesirable phenomenon of fluid suck-back. The observation prompted researchers at Walter Reed Army Institute of Research along with engineers at the Medical Equipment Development Laboratory at Fort Totten (MEDL) with the task of remedying the problem. By 1959, the DoD developed a new multi-use nozzle jet injector (MUNJI) that was intended to be an improvement over previous models. The device was called the Automatic Jet Hypodermic Injection Apparatus, or more commonly known as the Ped-O-Jet.

Lt. Colonel Abram Benenson, who oversaw the use of jet injectors within the DoD, acknowledged the collaborative work that birthed the Ped-O-Jet in a 1959 paper:

“[S]ince July 1957, we [Benenson and Lt. Col. Robert Lindberg] have been responsible for the development of jet injectors for immunization. Our field and laboratory studies depended on the efforts and support of Captain Adrain D. Mandel and Mr Charles E. Buckler; engineering support was furnished by the Medical Equipment Development Laboratory, Fort Totten, New York, where the basic principle was improved into the current multidose jet injector” (emphasis added) (Benenson, 1959).


Aaron Ismach, the inventor of the Ped-O-Jet and a civilian engineer at MEDL, reported that previous MUNJIs of the 1950s allowed for fluid suck-back. Ismach’s patent, filed December 14th of 1959, stated, “unlike most earlier hypodermic jet injection guns, the instant invention is free from 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” (Ismach, 1962). The Press-O-Jet would be one of the “earlier hypodermic jet injection guns” that Ismach was referencing.

Ismach’s patent specifically acknowledged the potential of fluid suck-back occurring when cocking the gun but states a ball check valve, located within the nozzle head, prevents this from happening. “The ball check valve 44 serves to prevent the entry of any air or suckback of any fluid during the loading cycle of the vaccine pump…” (Ismach, 1962).

From Ismach’s assertion the issue of fluid suck-back clearly rests upon the efficacy of the ball check valve. To gain an understanding of how Ismach improved upon the ball check valve, Jet Infectors compared the patents of the Press-O-Jet and Ped-O-Jet. One noticeable difference stands-out—the ball check valve on the Ped-O-Jet was spring-loaded to help keep it shutt, while the Press-O-Jet did not contain a spring.

The patent for the Press-O-Jet states, “Return flow of the inoculant through the bore 23 of plunger 22 is prevented by means of ball check valve 25.” Yet, the patent also notes that the ball check valve merely rests between two spaces without any reference of a spring: “A gasket 34 is interposed between the nose 33 and the end of plunger 22 and acts both as a seal and also as a retainer for the ball 25” (emphasis added) (Ziherl, 1958).

The diagram from the Press-O-Jet patent shows the ball check valve (number 25) resting between two partitions with no zigzagged line to indicate a spring.

Press-O-Jet ball check valve #25

(Ziherl, 1958)

Whereas the patent for the Ped-O-Jet clearly states the ball check valve is spring-loaded. “The ball check valve 44 serves to prevent the entry of any air or suckback of any fluid during the loading cycle of the vaccine pump, but the spring pressure on this valve 44 is light enough to be easily overcome during the firing or ejection cycle of the vaccine pump” (Ismach, 1962).

The diagram from the Ped-O-Jet patent shows the ball check valve (number 44) is retained by a spring, as indicated by the zigzagged line.

Ped-O-Jet Ball Check Outlet Valve #44

(Ismach, 1962)

The lack of spring-loaded ball check valve could be the reason the DoD had observed the Press-O-Jet to improperly work at times. “The failure of the ball check valve in the forward end of the plunger system to seat properly causes the gun to deliver less than the measured dosage and requires a metal lathe to gain access to the ball valve” (Anderson et al., 1958).

Even if the ball was properly seated within the counterbore the lack of resistance from a spring could account for the systemic fluid suck-back observed by Ismach.

The question now becomes did the spring-loaded ball check valve within the Ped-O-Jet prevent fluid suck-back?


As subsequent research reveals, the Ped-O-Jet still succumbed to fluid suck-back. Ismach’s assertions were nothing more than puffing statements.

  • In 1977, CDC’s Hepatitis Laboratories Division conducted safety testing on the Ped-O-Jet. The researchers observed a drop of fluid remained on the injector nozzle after firing and would disappear back into the nozzle orifice within 3 to 5 seconds. The researchers concluded, “These manipulations causing disappearance of the fluid drop are common during clinical use of the jet injector” (CDC, 1977).
  • Weniger, Jones and Chen recalled CDC’s 1977 investigation of the Ped-O-Jet, stating, “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).”
  • In 1994, the CDC retested the safety of the Ped-O-Jet. After artificially contaminating the underbelly of a shaved rabbit with Hepatitis B surface antigen (HBsAg), a sterile Ped-O-Jet was placed upon the site and administered an injection. The subsequent injection was fired into a vial and tested for HBsAg. The results found the ejected fluid of the next shot fired was positive for HBsAg in 19 out of 50 (38%) of the samples (Grabowsky et al., 1994). Cross-contamination of HBsAg from the skin surface to the ejectate of the subsequent shot was due to either fluid suck-back or retrograde flow.
  • The CDC collaborated with American Jet Injector Corporation and the University of Florida to test the safety of the Am-O-Jet, a MUNJI device. The Am-O-Jet was an identical design of the Ped-O-Jet. Within this study the researchers admit the check-valve had been redesigned; thus further implicating the inherent design faults of previous Ped-O-Jet models. It is noteworthy to add, the researchers found rates of contamination were significant with the Am-O-Jet (Sweat et al., 2000).

These reports document that jet injectors—including the most widely used jet injector, the Ped-O-Jet—allowed contaminates upon the nozzle orifice to be sucked into the internal fluid pathway and infect the next dosage to be fired. Despite attempts to resolve the problem with the ball check valve, fluid suck-back still occurred and has been continuously reported upon through-out the past 60-years.



  • (Anderson, Lindberg, & Hunter, 1958) Anderson EA, Lindberg RB, Hunter DH. Report of large-scale field trial of jet injection in immunization for influenza. JAMA 167:549–552, 1958.
  • (Benenson, 1959) Benenson AS. Mass immunization by jet injection. In: Proceedings of the International Symposium of Immunology, Opatija, Yugoslavia, 28 September—1 October 1959 (International Committee for Microbiological Standardization, Secton of the International Association of Microbiological Societies). Zagreb: Tiskara Izdavackog zavoda Jugoslavenske akademije; 1959;393–399 [Library of Congress QW 504 I60p 1959].
  • (CDC, 1977) CDC. DHEW Memorandum: Informal Quarterly Report of October-December 1977. From: Special Investigations Section (Petersen NJ, Bond WW, Carson LA) to: Deputy Director (Favero MS), Hepatitis Laboratories Division, Phoenix, AZ (unpublished).
  • (Grabowsky et al., 1994) Grabowsky M, Hadler SC, Chen RT, Bond WW, de Souza Brito G. Risk of transmission of hepatitis B virus or human immunodeficiency virus from jet injectors and from needles and syringes. Unpublished manuscript draft, dated January 3, 1994.
  • (Ismach, 1962) Ismach, Aaron. “Multi-dose jet injection device.” United States Patent 3,057,349. 9 October 1962.
  • (Sweat et al., 2000) Sweat JM, Abdy M, Weniger BG, Harrington R, Coyle B, Abuknesha RA, Gibbs EP. Safety testing of needle free, jet injection devices to detect contamination with blood and other tissue fluids. Ann NY Acad Sci 2000;916(31):681-682.
  • (Weniger, Jones & Chen) Weniger BG, Jones TS and RT Chen. “The Unintended Consequences of Vaccine Delivery Devices Used to Eradicate Smallpox: Lessons for Future Vaccination Methods.” National Center for Immunization & Respiratory Diseases. [Poster Presentation].
  • (Ziherl, 1958) Ziherl, Frank. “Multiple Injection Inoculator Instrument.” United States Patent 2821193. 28 January 1958.


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Faulty Design Created Inherent Risks – Retrograde Flow

Retrograde flow, also commonly referred to as black flow, is the undesirable phenomenon in which fluid, mixed with tissue cells, bodily fluid and blood, moves up the jet stream and enters the jet injector, contaminating the internal fluid pathway and drug reservoir.

The following illustrations demonstrate this concept. In the first image, the jet injector is actuated and the jet stream is emitted from the nozzle.

Jet Infectors - Retrodgrade Flow 1

In this image, the jet stream is deposited into the arm.

Jet Infectors - Retrograde Flow 2

Near the end of jet injection process, the pressure of the jet stream impinging the skin would be less than the pressure of the fluid deposited within the newly constructed hole in the vaccinee’s arm. Since the jet stream was too weak to further deepen the hole, it moved backwards and flowed out of the hole and back into the jet injector. This would be an expected phenomenon in almost every jet injection due to the continuous depletion of pressure. The image below demonstrates the multi-directional flow, in which tissue cells, blood and bodily fluids, flowed into the jet injector orifice.

Jet Infectors - Retrograde Flow 3


And where is the evidence?


© Jet Infectors, 2016 – 2018

Jet Injector Manufacturers Acknowledge Retrograde Flow

Linda D’ Antonio, spokeswoman for the now defunct Association of Needle-Free Injection Manufacturers, stated in a news article, “With the older style jet-injection devices, it was possible for blood to be drawn back into the nozzle…that blood then could be passed to the next person” (Snowbeck, 2001). Here an industry trade association made-up of 19 jet injector manufacturers, whose aim was to “promote understanding and advancement of needle-free injection technology, provide news and communication, and represent the industry to regulatory and technical standards organizations and the public” (CDC, 2006) admits to inherent design faults that permitted the transmission of blood to subsequent recipients.

Although this was not the only admission of a design flaw by the industry. Throughout the years, various manufacturers and engineers had acknowledged back flow, reflux, and back leak. All of these terms refer to retrograde flow.

Kenneth Dunlap acknowledged “flow back” within his 1991 patent for a disposable nozzle assembly jet injector. Dunlap stated,

In the case of the prior art needleless injectors heretofore described, during the administration of an injection, the fluid jet driven at high pressure through the patient’s skin may result in some minor amount of bleeding and because the nozzle assembly of the jet injector is pressed firmly against the skin at the moment of release and for a short time thereafter, there is a possibility that blood might flow back into the ejection orifice to contaminate the nozzle. As such, to avoid cross-contamination of blood between different patient’s being treated in a hospital or clinic situation, it would heretofore be necessary to disassemble the drug injector and sterilize those portions of the assembly that could conceivably retain contaminated blood (U.S. Patent 5062830).

Sergio Landua wrote about “blood reflux” within his 1998 patent for a disposable syringe jet injector.

It is considered that replacing the nozzle tip alone after each injection is not sufficient to guarantee complete elimination of cross contamination between patients, since by particles of blood reflux during the injection, viruses or pathogens may be carried on to the inside of the dose chamber, and therefore contaminate the following medication dose to be injected in the next patient (U.S. Patent 5782802).

Bruce Joseph Roser described “reflux flow” within his 2003 patent for a disposable injection device. Roser explained,

It appeared that high pressure occurring in the tissues, which were suddenly distended by the injection, coincided with falling pressure inside the jet injector. Ultimately, this caused a reflux flow or “sucking-back” of tissue fluid into the injector. Because of this serious drawback, single-use vials which insert into the mechanical injector were developed (U.S. Patent 6602222).



  • (CDC, 2006) Centers for Disease Control and Prevention. Needle-free injection technology. Department of Health and Human Services. 12 September 2006. Accessible at: https://web.archive.org/web/20061225084649/http://www.cdc.gov/nip/dev/jetinject.htm.
  • (Snowbeck, 2001) Snowbeck C. Reviving an old technology for large-scale vaccination. Post-Gazette. 20 November 2001. Accessible at: http://old.post-gazette.com/healthscience/20011120hjet2.asp.
  • (U.S. Patent 5062830) Dunlap KW. “Dry Disposable nozzle assembly for medical jet injector.” United States Patent 5,062,830. 5 November 1991.
  • (U.S. Patent 5782802) Landau S. “Multiple use needle-less hypodermic injection device for individual users.” United States Patent 5,782,802. 21 July 1998.
  • (U.S. Patent 6602222) Roser BJ. “Disposable injection device.” United States Patent 6,602,222 B1. 5 August 2003.

© Jet Infectors, 2016 – 2018
Fair Use Notice (17 U.S.C. § 107)

Research Documented Retrograde Flow

Although the concept of retrograde flow may seem hard to believe, the phenomenon has been independently validated by various researchers from the USA, Netherlands, Russia, and England over the past 50 years. The phenomenon has been described in scientific literature with terms such as reflux, back flow and back leak.

Retrograde flow was initially observed in the first multi-use nozzle jet injector, the Press-O-Jet, during the 1950s. Elisberg, McCown and Smadel (1956) reported, the “backflow of inoculum mixed with the subject’s bodily fluids,” however it was their belief that “the precautionary quick withdrawal of the jet injection syringe immediately after the inoculation is finished prevents contamination of the nozzle with agents which might transmit a blood-borne infection.” Contrary to Elisberg, McCown and Smadel’s belief, subsequent research has shown prompt removal of the jet gun failed to stop cross-contamination within the half second it took to administer the vaccination.

Robert Hingson acknowledged a “back leak” of fluid within his 1963 paper in the Military Medical Journal. Hingson wrote, “Because of the need for readjustment by the tissues which so suddenly receive the 1 cc. injection, we recommend keeping the injector nozzle compressed tightly against the injected site for one second after injecting, to minimize back leak” (Hingson, Davis & Rosen, 1963). Hingson’s belief was the jet injector would act as a barrier, stopping the back flow of fluid, and give time for the fluid to absorb into the surrounding tissue. However, Hingson failed to test if the “back leak” would breach the nozzle orifice and contaminate the inside of the jet injector.

Dutch researchers observed retrograde flow during the 1980s. Brink and colleagues (1985) found cross-contamination of a highly infectious virus occurred within their study on mice despite the lack of visual bleeding at the injection site. The researcher’s hypothesized, “Probably the enormous tissue pressure caused a splashback of the injected fluid. This retrograde stream could be responsible for the transport of virus particles.” The researchers further stated investigations should be conducted to see if this phenomenon occurs in humans.

Russian researchers, Evstigneev and Lukin, noted retrograde flow within their investigations during the 1990s. The researchers wrote, “infection is possible because of retrograde flow of vaccine preparation which just has mixed with tissue liquid of a previous patient or taking into account a continuous contact of an injector head with patient’s skin during injection” (Evstigneev & Lukin, 1994).

Researchers from Kalamazoo College investigated the potential for cross-contamination with the Syrijet, a multi-use nozzle jet injector made from the same manufacturer as the Ped-O-Jet. In assessing the transference of microbial pathogens during the injection process, Suria and colleages (1999) found, “the degree of backflow and resulting contamination increased with increasing ejection volume setting, from lowest (0.06 cm3) to highest (0.30 cm3).” Suria observed the greater the volume the greater degree of internal contamination from retrograde flow. Suria also noted swabbing the nozzle of the jet injector did not remove internal contamination.

Joy Baxter and Samir Mitragotri both described the mechanical workings of jet injection in their 2006 paper. Baxter, a researcher for Unilever Research and Development, and Mitragotri, a chemical engineer at Harvard University, wrote, “Backflow of the jet is observed during hole formation if the volumetric rate of hole formation in the skin is smaller than the volumetric flow rate of the jet liquid into the skin” (Baxter & Mitragotri, 2006).

In October of 1998, the WHO conducted a simulated field trial to assess the degree of blood transmission via Ped-O-Jet injectors. Swabbing the nozzle of the Ped-O-Jet did not eliminate but only slightly reduced the degree of contamination. This finding indicates contamination was present inside the injector’s internal fluid pathway, beyond the reach of swabbing the nozzle, due to retrograde flow (Hoffman et al., unpublished).

Hoffman also found retrograde flow within his laboratory investigations of four different jet injectors. In fact, the researcher found retrograde flow was a natural phenomenon within the jet injection process and referred to it as “ballistic contamination” (Voelker, 1999). Hoffman thoroughly explained the process within his paper.

…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 (Hoffman et al., 2001).

The Program for Appropriate Technology in Health (PATH) assessed the degree of contamination with jet injectors during the mid-1990s. The tests sought to detect contamination in three areas: 1) On the surface of the skin that was injected, 2) upon the surfaces of the jet injector that had contact with skin, and 3) in the ejectates, or rather the next dose fired. The tests “showed systematic contamination of both the ejectate and the internal fluid pathway” (WHO, 1997). Contamination of the internal fluid pathway could only have occurred due to either fluid suck-back or retrograde flow.

PATH redeveloped jet injectors to avoid the risk of cross-contamination by implementing a single-use protector cap to shield the jet injector from splash-back. However, as safety testing showed, the protector cap was not infallible. Kelly and colleagues (2008) found the Hepatitis B virus cross-contaminated through the protector cap and into the next dosage to be fired. Cross-contamination could only have occurred by the phenomenon of retrograde flow.



  • (Baxter & Mitragotri, 2006) Baxter J, Mitragotri S. Needle-free liquid jet injections: mechanisms and applications. Expert Rev Med Devices Sep 2006;3(5):565-74.
  • (Brink et al., 1985) Brink PRG, van Loon AM, Trommelen JCM, Gribnau FWJ, Smale-Novakova IRO. Virus transmission by subcutaneous jet injection. J Med Microbiol. December 1985; 20(3): 393-397.
  • (Elisberg, McCown, & Smadel, 1956) Elisberg BL, McCown JM, Smadel JE. Vaccination against smallpox. Jet injection of chorio-allantoic membrane vaccine. J Immunol 1956;77(5):340-351.
  • (Evstigneev & Lukin, 1994) Evstigneev VI, Lukin EP. The safety of the jet (needle-free) injection. Military Medical Journal (Russia) Jul 1994; (7):38-39, 79.
  • (Hingson, Davis, & Rosen, 1963) Hingson RA, Davis HS, Rosen M. The historical development of jet injection and envisioned uses in mass immunization and mass therapy based upon two decades’ experience. Military Medicine 128:516–524, 1963.
  • (Hoffman et al., unpublished) Hoffman PN, Abuknesha RA, Andrews NJ, Brito GS, Carrasco P, Weckx LY, Moia LJMP, Silva AEB, Lloyd J. A field trial of jet injector safety in Brazil. (unpublished).
  • (Hoffman et al., 2001) Hoffman PN, Abuknesha RA, Andrews NJ, Samuel D, Lloyd JS. A model to assess the infection potential of jet injectors used in mass immunisation. Vaccine. 16 July 2001;19(28-29):4020-4027.
  • (Kelly et al., 2008) Kelly K, Loskutov A, Zehrung D, Puaa K, LaBarre P, Muller N, Guiqiang W, Ding H, Hu D, Blackwelder WC. Preventing contamination between injections with multi-use nozzle needle-free injectors: a safety trial. Vaccine (2008) 26, 1344-1352.
  • (Suria et al., 1999) Suria H, Van Enk R, Gordon R, Mattano LA Jr. Risk of cross-patient infection with clinical use of a needleless injector device. Am J Infect Control. 1999 Oct; 27(5):444-7).
  • (Voelker, 1999) Voelker R. Eradication Efforts Need Needle-Free Delivery. JAMA May 26, 1999;281(20):1879-1881.
  • (WHO, 1997) World Health Organization. Steering group on the development of jet injection, Geneva, 18-19 March 1997. Geneva: World Health Organization, Global Programme on Vaccines and Immunizations, document, 1997;1-37.

© Jet Infectors, 2016 – 2018
Fair Use Notice (17 U.S.C. § 107)

Faulty Design Created Inherent Risks – Splash-Back

Splash-back refers to contamination upon the nozzle of the jet injector. This undesirable phenomenon occurs when the jet stream impinges the skin during hole formation, in which debris—consisting of fluid, tissue cells, blood, and bodily fluid—splashes back onto the jet injector nozzle and possibly into the nozzle orifice.

Splash-back is more likely to occur when the nozzle orifice is not pressed firmly against the skin or with jet injectors that have a spacer which creates a gap in between the nozzle orifice and skin.

The following illustrations demonstrate the concept. In the first image, the jet injector is actuated and the jet stream is emitted from the nozzle orifice, as demonstrated with the blue arrow.

Jet Infectors - Splash-back 1

In this image, the jet stream penetrates the skin, initiating hole formation. This will cause debris, as mentioned above (fluid, tissue cells, blood and bodily fluids), to splatter, as demonstrated with the red arrow.

Jet Infectors - Splash-back 2

Since the nozzle of the jet injector is in the immediate splatter field it will become contaminated, as demonstrated below.

Jet Infectors - Splash-back 3


“Where is the proof?” you may question. Glad you asked.



© Jet Infectors, 2016 – 2018

Research Documented Splash-back

Splash-back has been previously reported upon in scientific studies. A 1966 article titled, Vaccination by Jet Injection, published in the British Medical Journal stated, “There is no risk of cross-infection unless the face of the injector is contaminated with blood or tissue juices” (Anonymous, 1966). Although studies have demonstrated the nozzle of the jet injector indeed becomes contaminated during jet injection.

  • Hoffman and colleagues (2001) observed the nozzle and internal fluid pathway became contaminated during the jet injection process amongst several brands of jet injectors, including the Ped-O-Jet and Med-E-Jet. He termed this phenomena as ballistic contamination, whereupon the force of impact caused a release of pressure which expelled debris away from the site of impact (Voelker, 1999). With the jet injector being directly behind the site of impact it is a prime target to becoming contaminated.
  • Lipson and colleagues (1958) assessed if the antibody response to a poliomyelitis vaccine via jet injection would be comparable to needle and syringe. In the study, thirty-four children received two doses of polio vaccine via a handheld Press-O-Jet injector and twenty-seven children received one dose of vaccine by needle. Lipson stated, “We observed blood on the nozzle of the jet injector on two different occasions.” This means in 3 percent of the injections blood was observed on the jet injector nozzle, indicating the nozzle became contaminated due to splash-back.
  • Kutscher and colleagues (1962) warned of splash-back within their paper. “The Hypospray unit itself is not sterilized although the head can and should be disinfected,” stated the researchers. If the patient’s arm is not properly held “some portion of the injected material may rebound and not attain its target” (emphasis added). In other words the injected material would splash back onto the jet injector.
  • Dr. Sol Roy Rosenthal studied the transference of blood via the Hypospray Multidose jet injector amongst children at two schools. Observations from the first school found the jet injector produced “much bleeding.” Overall the study found in 17 percent of the vaccinations of school children there was enough blood on the jet injector nozzle to transmit blood-borne pathogens (Rosenthal, 1967).
  • Horn, Opiz and Schau (1975) observed splash-back through their investigations of the Hypospray Multidose and warned of the risk this posed in spreading hepatitis. Horn stated,

We were able to demonstrate by direct staining of material obtained from the nozzle, that this part of the injector becomes contaminated with material originating in human white blood corpuscles. These findings are very similar to those of Hughes with syringes and have an obvious implication in relation to the transfer of hepatitis virus by jet injectors (Horn, Opiz & Schau, 1975).

This research serves as evidence that the nozzle face of the jet injector becomes contaminated during the injection process.



  • (Anonymous, 1966) Anonymous. Vaccination by Jet. Br Med J December 31, 1966: 1610.
  • (Hoffman et al., 2001) Hoffman PN, Abuknesha RA, Andrews NJ, Samuel D, Lloyd JS. A model to assess the infection potential of jet injectors used in mass immunization. Vaccine 19 (2001): 4020-4027.
  • (Horn, Opiz & Schau, 1975) Horn H, Opiz B, Schau G. Investigations into the risk of infection by the use of jet injectors. Health and Social Serv J 85:2396–2397, 1975.
  • (Kutscher et al., 1962) Kutscher AH, Hyman GA, Zegarelli EV, Dekis J, Piro JD. A comparative evaluation of the jet injection technique (Hypospray) and the hypodermic needle for the parenteral administration of drugs: a controlled study. Am J Med Sci 1962;54:418-420.
  • (Lipson et al., 1958) Lipson MJ, Carver DH, Eleff MG, Hingson RA, Robbins FC. Antibody response to poliomyelitis vaccine administered by jet injection. Am J Public Health 1958;48(5):599-603.
  • (Rosenthal, 1967) Rosenthal SR. Transference of blood by various inoculation devices. Am Rev Respir Dis. October 1967; 96(4):815-819.
  • (Voelker, 1999) Voelker R. Eradication Efforts Need Needle-Free Delivery. JAMA May 26, 1999;281(20):1879-1881.


© Jet Infectors, 2016 – 2018
Fair Use Notice (17 U.S.C. § 107)

PATH’s Fluorescein Testing on Ped-O-Jet Injectors

The Program for Appropriate Technology in Health (PATH), funded by the Bill and Melinda Gates Foundation, has been a major contributor in the development of safer jet injection technology. Although during the development of safer, next generation jet injectors, PATH needed to assess how bad were the Ped-O-Jet injectors.

Around 2003-2004 PATH conducted a “simple” test to assess the safety of the HSI-500, a prototype jet injector manufactured by Felton International, Inc. The “simple” test was an in vitro fluorescein contamination test, which made any contamination visible due to the use of a fluorescein dye. The highly concentrated fluorescein dye was used as a surrogate for high titer Hepatitis B infection (FDA, 2005).

PATH - Example of a Positive Fluorescein Sample

(Zehrung, 2003)

“The fluorescein assay really exceeds the PCR [polymerase chain reaction] methods in terms of a detection limit,” explains Darin Zehrung, the Associate Technical Officer at PATH. “So it’s very sensitive, it’s very specific in terms of an assay. And we believe a good surrogate aside from human testing to demonstrate cross-contamination safety” (FDA, 2005).

For this experiment PATH used the Ped-O-Jet injector as a comparative model. The HSI-500 and the Ped-O-Jet injector were both sterilized and administered an injection into a test fixture containing a fluorescein dye. Each of the jet injectors then fired the subsequent shot into vials and the ejectates were evaluated. The threshold for contamination was defined as detection of more than 10 picoliters within the 0.5 cc sample. Results for the Ped-O-Jet found 75 out of 100 (75%) samples contained more than 10 picoliters of fluorescein. Results for the HSI-500 found no contamination (Zehrung, 2004). These results indicated the Ped-O-Jet cross-contaminated a sufficient volume of fluorescein from the infected host to the next dose.

PATH had conducted performance and safety evaluations on the Ped-O-Jet, as noted within these pictures. Note in the photograph on the right, a drop of fluid remains on the nozzle tip post-injection.

PATH's Performance Testing of Ped-O-Jet

(Zehrung, 2003)


In March of 2004, PATH attended a CDC/WHO conference on jet injector safety which focused on establishing safety requirements for disposable-cartridge jet injectors. The meeting delved into evaluating several unknown factors. “The questions are how infectious is blood? How do we measure it? How do you model the risk? What level of risk is acceptable?” (FDA, 2005). Members of the conference were in agreement that quantities smaller than 10 picoliters could be infectious.

Based upon this conclusion, PATH altered the threshold of contamination from 10 picoliters to 0.04 picoliters. PATH conducted their fluorescein test a second time using the new 0.04 picoliter threshold level. Results demonstrated cross-contamination with the Ped-O-Jet but no cross-contamination with the HSI-500 jet injector.

Mr. Zehrung explained the results of the experiment in detail at a 2005 FDA conference on jet injector safety. For reasons unknown Mr. Zehrung refers to the Ped-O-Jet as a “first generation MUNJI device.” Although in other sources, he disclosed this was in fact the Ped-O-Jet injector (Zehrung, 2003; Zehrung, 2004).

Mr. Zehrung: So you may not be able to see these pictures. This is a first generation MUNJI device. I think that those are familiar with these technologies know what that device would be called. And you can see after injection into the test fixture, there is contamination at the injection site. There’s a combination of splash back as well as contact contamination during the injection process. You see that it’s contaminated with the fluorescein dye.
The same is true for the protector cap injector. This is the protector cap on the nozzle face itself.  It’s hard to see in this photo, but this protector cap post injection into the test fixture is also contaminated. But the down stream sample collected after injection into the text fixture is demonstrated to be free of cross- contamination.
Next slide.
So this is a slide showing the comparison of first generation MUNJI testing with this method versus a protector cap injector. These are the number of samples. So for a 100 samples with the first generation MUNJI device, all were contaminated, a 100 percent with an average contamination rate of 268 picoliters. In comparison with the protector cap injector for 300 samples, all samples were free of cross-contamination (FDA, 2005).

This is worth repeating. Mr. Zehrung presented images from the test which demonstrated the Ped-O-Jet as well as the injection site were both contaminated with fluorescein dye. This type of contamination is known as splash-back. The protector cap for the PCNFI was also contaminated with fluorescein. These results demonstrate that no matter the model or generation of jet injector gross-contamination upon the injection site and the nozzle are natural phenomenon of jet injection.

Results of the Ped-O-Jet found contamination in 100 out of 100 (100%) of the samples. The average volume of fluorescein contamination within the ejectates was 268 picoliters. This shows gross cross-contamination by the Ped-O-Jet. Mr. Zehrung stated of these results, “we believe that this [i.e., the fluorescein testing] is a very useful and powerful method to demonstrate contamination risk with the earlier devices” (FDA, 2005).

PATH’s fluorescein testing of the Ped-O-Jet further illuminates the degree of contamination these devices posed.


  • (FDA, 2005) FDA. General Hospital and Personal Use Devices Panel of the Medical Devices Advisory Committee. August 9, 2005. 35th Conference. Washington, D.C.
  • (Zehrung, 2003) Zehrung D. PATH’s Experience from Jet Injector R&D and Field Assessment in Developing Countries. Presentation for Innovative Administration Systems for Vaccines. Rockville, Maryland. 18 December 2003.
  • (Zehrung, 2004) Zehrung D. Jet Inject for Mass Immunization: Design Update and Safety Testing Strategy. Presentation for Global Vaccine Research Forum. 10 June 2004.

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Experts Claim Cases of Jet Injector Transmission Would Not be Documented

Numerous professionals have stated it would be difficult to impossible to document transmission via jet injectors. Hepatitis C most often progresses asymptomatically and would not be detectable without ongoing active surveillance. However, Hepatitis C was not identified until 1989 and a test to identify the virus was not created until 1992, therefore it would have been impossible to document any incidents of transmission before 1992.

  • Dr. Bruce Weniger, formerly the Lead Researcher on Vaccine Technology within the CDC and known as Mr. Jet Injection, is one of, if not the, leading expert on jet injectors. In Dr. Weniger’s professional opinion, he states,

MUNJIs are inherently unsafe. Their re-use without intervening sterilization of fluid pathways which may be exposed to patient blood or tissue fluid violates established principles that apply to other critical medical devices. One cannot rely of the absence of documented cases of disease transmission beyond the California outbreak. It is unlikely that routine post-marketing surveillance would link sporadic cases to prior MUNJI use (Weniger, 2005).

  • In 1977 the Hepatitis Laboratories Division of the Center for Disease Control secretly conducted safety testing upon the Ped-O-Jet injector. The researchers called for “specifically designed prospective seroepidemiologic studies” to assess the risk of hepatitis transmission via jet injectors (CDC, 1977). Yet no one heeded the call.
  • In 1994 researchers within the CDC retested the safety of the Ped-O-Jet Injector. They noted, “The detection of rare, silent transmission would have been difficult, however, and likely to have been missed without active surveillance” (Grabowsky et al., 1994). Therefore, just because there were no documented cases does not mean transmission of blood-borne pathogens did not occur.
  • In 1996 the CDC and WHO held a conference on jet injector safety, in which participants had noted, “For an asymptomatic infection like hepatitis B, serosurveys would be required to detect transmission of the virus; in the absence of such data, it is impossible to state with any assurance that transmission has not occurred” (Fields, 1996). Hepatitis C most often progresses asymptomatically as well and therefore would not be detectable without ongoing active surveillance.
  • The Armed Forces Epidemiological Board, which is an expert advisory board of civilian physicians and scientists that assists the Department of Defense with medically related issues, stated within a January 9th of 1998 memorandum that no active prospective surveillance studies have been performed to uphold the safety record of jet injectors (AFEB, 1998).


  • (AFEB, 1998) Armed Forces Epidemiological Board. Recommendation on Jet Injectors. AFEB (15-1a) 98-6. January 9, 1998.
  • (CDC, 1977) CDC. DHEW Memorandum: Informal Quarterly Report of October-December 1977. From: Special Investigations Section (Petersen NJ, Bond WW, Carson LA) to: Deputy Director (Favero MS), Hepatitis Laboratories Division, Phoenix, AZ (unpublished).
  • (Fields, 1996) Fields R. Participation in Meeting: Jet injectors for immunization; current practice and safety; improving designs for the future. WHO/CDC Meeting. Atlanta, GA. 2-3 October, 1996. Available at: http://pdf.usaid.gov/pdf_docs/PNABZ997.pdf.
  • (Grabowsky et al., 1994) Grabowsky M, Hadler SC, Chen RT, Bond WW, de Souza Brito G. Risk of transmission of hepatitis B virus or human immunodeficiency virus from jet injectors and from needles and syringes. Unpublished manuscript draft, dated January 3, 1994.
  • (Weniger, 2005) Weniger B. Safety of Multi-use-nozzle Jet Injectors (MUNJIs) for Bloodborne Pathogen Cross-contamination [draft]. Conference Notes. 7 August 2005.


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Dr. Sabin Warned of Hepatitis Risk From Jet Injectors in 1976

Dr. Albert Sabin, the creator of the oral polio vaccine, warned jet injectors could spread hepatitis in 1976. Several newspapers had reported upon Dr. Sabin’s comments.

During a meeting amongst health professionals planning a mass vaccination campaign for swine flu, Dr. Sabin interrupted a speaker to voice his concerns.

The York Daily Record reported in 1976, “Sabin…stood up during a speech by state epidemiologist Dr. Richard Parker to challenge the state and national strategy against swine flu.”

The article further stated, “Sabin also warned jet-injector guns could possibly spread disease during a mass immunization campaign” (York Daily Record, 1976).

In response to Dr. Sabin’s comments, the CDC purported that jet injectors are safe to use. The Salt Lake Tribune printed the following:

Defends Jet Gun Safety
Jet injector guns, which can inoculate up to 800 persons an hour, were being used in the immunization clinics. The CDC said that contrary to a charge by Dr. Albert Sabin, the discoverer of oral polio vaccine, the jet guns are safe to use and do not transmit any disease such as hepatitis (Salt Lake Tribune, 1976).

Yet the CDC did not conduct any safety testing upon the jet injector until 1977, in which the Hepatitis Laboratories Division did find the transmission of hepatitis via jet injectors was possible. See article – CDC’s Unpublished Jet Injector Studies – Part I

Dr. Sabin, like several others during his time, was correct to question the safety of jet injectors.

  • In 1962, the Eli Lilly Company warned, “If the nozzle becomes contaminated with blood or serum, it should be replaced or resterilized before further use to prevent the transmission of serum hepatitis virus or other infectious agents from one person to another.” See article – 1962 – Eli Lilly Warns of Hepatitis Transmission Via Jet Injection
  • In 1967, Dr. Sol Rosenthal studied the transference of blood between consecutive vaccinees when using a jet injector. Dr. Rosenthal stated, “It was reasoned that if the detection of the transference of erythrocytes (hemoglobin) or serum could be assayed, one might infer that the parenteral hepatitis agent would likewise be transferred” (Rosenthal, 1967).
  • In 1970, M.G. Kremer raised concern over the cross-contamination of serum hepatitis from jet injectors in the British Medical Journal. Kremer wrote, “The injector is not sterilized between injections, and in many cases it produces a small amount of bleeding at the injection site. The injector could thus become contaminated with blood, thus transmitting, for instance, hepatitis virus to subsequent patients” (Kremer, 1970).
  • During a 1971 National Institute of Health conference on tuberculosis vaccinations, the consensus from members was jet injectors do produce blood during the administering of vaccination and the possibility of transferring hepatitis cannot be excluded (DHEW, 1972). See article – 1971 NIH Conference Recognizes Bloody Jet Injectors Pose Risk For Hepatitis



  • (DHEW, 1972) Department of Health, Education and Welfare, Public Health Service, National Institutes of Health. Status of Immunization in Tuberculosis in 1971; DHEW Publication No. (NIH) 72-68, pp. 185-187. Washington, D.C., 1972.
  • (Kremer, 1970) Kremer MG. Jet vaccination [letter]. Brit Med J 1970; 4:303.
  • (Rosenthal, 1967) Rosenthal SR. Transference of blood by various inoculation devices. Am Rev Respir Dis. October 1967; 96(4):815-819.
  • (Salt Lake Tribune, 1976) Salt Lake Tribune. Swine Flu Drive Moves With Few Side Effects. Salt Lake City, Utah. 3 October 1976. pg. 2.
  • (York Daily Record, 1976) York Daily Record. Dr. Sabin Opposes Mass Swine Flu Shots. York, Pennsylvania. 23 September 1976. pg. 2.

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