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?


© Shaun Brown and Jet Infectors, 2016 – 2018

Research Documented Fluid Suck-back

During the 1950s, inventors noted the undesirable phenomenon of fluid suck-back in multi-use nozzle jet injectors. Yet despite attempts to resolve the problem, fluid suck-back has been continuously observed and reported upon through-out the past 60-years.

  • Anderson, Lindberg and Hunter (1958) observed a large-scale military field trial conducted upon sailors stationed at Naval Air Station in Norfolk, Virginia. The mass influenza vaccination campaign administered 20,145 injections with a Press-O-Jet injector between 1955 and 1956. Fluid suck-back was observed during the military vaccination campaign. “Another ball valve is located at the rear of the plunger assembly and, if improper seating occurs, will allow vaccine to be returned to the reservoir on each injection,” wrote the researchers.


  • Inventor of the Ped-O-Jet, Aaron Ismach, stated within his 1962 patent that his invention 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” (Ismach, 1962). His assertion reveals MUNJIs faced issues with check-valves. Subsequent research has revealed the Ped-O-Jet was no exception to this inherent design fault.


  • 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).


  • In 1974, Aaron Ismach developed an alternative jet gun injector in which the energy source was generated through hand-power rather than foot-power. Ismach’s patent purported to overcome the risk of fluid suck-back. “The check outlet valve serves to prevent the entry of any air or suck-back of any fluid during the loading cycle of the medicament chamber with the spring pressure on this valve sufficiently light to be easily overcome during the firing or ejecting cycle” (U.S. Patent 3805783).

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.



  • (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.
  • (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.
  • (U.S. Patent 3805783) Ismach A. “Hand Powered Hypodermic Jet Injector Gun.” United States Patent 3,805,783. 23 April 1974.
  • (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].


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


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?


© Shaun Brown and 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.

© Shaun Brown and 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 grossly failed to test if the “back leak” would 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.

© Shaun Brown and 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.



© Shaun Brown and 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.


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

Unsterile Mass Jet Injections: CDC Researchers Divulge Hazards of Ped-O-Jet Injectors During 1960s & 1970s Mass Vaccination Campaigns

During the 1960s and 1970s, the Communicable Disease Center (CDC) sent young men to traverse the globe in a noble effort to control outbreaks and eradicate viruses. Two of the most notable mass vaccination campaigns were the Smallpox Eradication Program and the Measles Control Program. Recently, the CDC has made accessible the interviews of these admirable men reflecting upon their travels. These interviews reveal the true first-hand accounts of how mass vaccination campaigns were conducted abroad and includes information previously not included within scientific studies. Their honesty has been greatly appreciated.


“We didn’t really use much sterile technique.”

Researchers recall the lack of sterilization within their interviews.

“The jet injector nozzle actually did press up against the skin,” said Dr. William Foege in a 2006 interview at CDC Headquarters in Atlanta, Georgia. “At that time, people were quite sure that there was no chance of cross-contamination, that the vaccine came out at high pressure, but we’ve subsequently changed our mind about this, and that’s why we don’t use jet injectors at this point” (Harden, 2006a).

Dr. Foege, the former Director of CDC from 1977-83, served in the Smallpox Eradication Program in Nigeria in his early years as a missionary and then as a CDC staffer. During his career he administered tens-of-thousands of jet injections and he now acknowledges that the previous understanding of jet injector safety was incorrect and jet injectors due, in fact, pose a risk of cross-contamination.

Another CDC researcher, Dr. Deane Hutchins, served in CDC’s Smallpox Eradication Program in Nigeria and Sierra Leone. Dr. Hutchins also described lack of sterilization.

I realized that you could train uneducated people to do a health program. For example, these vaccinators that we had had very little education. Sterile technique was still unheard of, and we didn’t really use much sterile technique. We did not clean off arms before people were vaccinated. We told the vaccinators that if they dropped the nozzle of the jet injector on the ground, clean it off with some alcohol or something. They would just brush it off and put it back on. We did studies to see if there were any adverse effects, and there was no significant increase in infections from this lack of sterile technique (Harrar, 2006).

Yet the tests to ascertain any adverse effects from the use of the Ped-O-Jets were not capable of testing for Hepatitis B, Hepatitis C or HIV at the time. In fact, these viruses were still unknown to mankind.

Dr. Stanley Foster, who served in CDC’s Smallpox Eradication Program in Nigeria and Bangladesh, stated in a personal interview with this author, “At that time the question was the effectiveness of the Ped-o-Jet not the risk of infection” (Foster, 2017).

CDC photographs have also captured the lack of sterilization during these vaccination campaigns. The following photograph captures a young child receiving a smallpox vaccination in Nigeria in 1969. Notice the mass vaccination is being conducted within a field and the vaccinator is bare foot. When the jet gun is stowed in the carrying case it rests next to the foot pedal. Therefore, any dirt on the pedal would fall and contaminate the jet gun. Also notice the second vaccinator, who is wearing a hat, is smoking a cigarette while he awaits to give a vaccination.

1969 Smallpox Vaccination in Nigeria - Lack of Sterilization

(Unknown, 1969)

This photograph, captured during a mass vaccination in Nigeria, documented bleeding at the injection site. Notice the young girl in the center of the photo, standing to the right of the vaccinator dressed in a white lab coat. The girl is holding her right bicep after receiving a Ped-O-Jet injection. Now notice the infant being held on the far right side of the image. Upon his bicep is a piece of cotton or cloth tinged with a droplet of blood.

Nigerian parents brought their children for smallpox vaccination


Locals Trained to Be Vaccinators

Local healthcare workers were trained in the use of the Ped-O-Jet, as shown in this 1968 photo of Nigerian healthcare workers after a training class. Dr. Hutchins had noted at certain times “uneducated” locals were trained to administer vaccinations (Harrar, 2006).

1968 Ped-O-Jet Training Class in Nigeria

(Unknown, 1968)


Speedy Injections

Dr. Foege described the haste at which the immunizations were given.

You set up a rhythm: grab the arm, step on the hydraulic lever, shoot, and the person would continue on. You could do a thousand people an hour, and I remember at one point doing a prison in eastern Nigeria, where they had the inmates lined up, and they were actually pushing them through by hitting them with sticks. I did 600 people in twenty minutes, because it was such a regimented line that you could just grab people and do them so fast. At one point, I recall doing over 11,000 smallpox immunizations in one day. So, yes, you could do this very quickly (Harden, 2006a).

Bob Baldwin, who served as CDC’s Regional Operations Officer in French-speaking West Africa, remembers the chaotic crowds.

I do remember being out there and immunizing kids with a ped-o-jet in each hand, smallpox in this gun and measles vaccine in this gun, and I’m pushing down on the foot pedal for this gun, to charge it and give the kid an immunization, and the other one with the other hand. And they’re crowding around, and crowding to the point where you couldn’t work. The Africans were so afraid that you were going to run out of vaccine, that their children weren’t going to get immunized, that they would just…And so I had to, a number of times I had to stop and just say to the headman or to the chief, you’ve got to get the people lined up, in a line. I can’t work here. I mean, if I can’t work, I can’t immunize them (Diallo, 2006).

Unbeknownst to Mr. Baldwin holding a jet injector in each hand was an improper technique. The vaccinator must hold the jet gun in one hand and use his or her opposite hand to support the vaccinee’s arm as well as to pull the flesh tight to receive a proper vaccination.


Frequent Maintenance Repairs

Despite the effectiveness and efficiency of the Ped-O-Jets, the guns required frequent maintenance and repairs.

Dennis Olsen, who served as an Operations Officer for CDC’s Smallpox Eradication Program in Liberia, recalled the vast amount of training that went into learning how to repair the Ped-O-Jet injectors.

I spent a lot of time in training programs because we were using Ped-O-Jet equipment, and so we spent a lot of classroom time in operations maintenance of it. And, of course, we had to wait for supplies to come in (Drew, 2006a).

David Bourne, who assisted in CDC’s mass vaccination campaign in Ethiopia while serving as a Peace Corps volunteer said the jet guns “often broke down especially in the desert” (Decker, 2008).

Another researcher described the poor-quality with which the Ped-O-Jet was made. “Unfortunately, the Ped-O-Jets were not made for the military. They were made for CDC by a firm in New York, and I don’t think they were up to the same quality level,” said Jay Friedman, who served as CDC’s Operations Officer in the West African nations of Mali, Gabon, and Nigeria (Drew, 2006b).

However, Mr. Friedman is misinformed. The Scientific Equipment Manufacturing Corporation (SEMCO) manufactured both the electric model known as the Multidose, and the non-electric foot pedal known as the Ped-O-Jet. When SEMCO sold-off the devices to Vernitron Medical Products, both devices were still manufactured under one company. Moreover, the U.S. military not only invented but also used both the electric and foot-operated models. Therefore his assumption that the jet injectors were not being made to the same quality is inaccurate. His personal testimony about the functioning of the Ped-O-Jet injectors and the quality of their parts, however, carries valuable weight and insight.

Mr. Friedman continued to say,

The guns would break-not so much break, as their internal valves and springs would wear out or get stuck. The nozzles would clog, for which we had special wires to ream them out. And especially the pedal, the pedal pump. I think they were made of aluminum with Teflon O-rings acting as piston rings. And this aluminum, being a soft metal, would wear out very quickly. Being an ex-mechanic, I had to fix them all the time, although I trained Malians to work on them, which is not very difficult. And we spent a lot of time fixing these Ped-O-Jets. In fact, in Mali, we had 1 guy, a vaccinator, assigned full-time to work on Ped-O-Jets that were being used out in the field. So we had to transport them back to the capital to have this guy work on them. The simple repairs could be done in the field. But any time the pedal pump broke, you had to send it in. You had to re-machine the whole piston when that happened… (Drew, 2006b).

The following CDC photograph shows Operations Officer, Lloyd Wade, repairing a Ped-O-Jet in 1967 while smoking a cigarette.

1967 Ped-O-Jet Repair While Smoking Cigarette

(Robbins, 1967)


“Lack of good communication…”

Bob Baldwin also recalled how the Ped-O-Jets would breakdown and the urgency of acquiring the parts to fix the guns for the next campaign.

…the lack of good communications in those days. I mean, back and forth to where you needed, either to alert people that you were coming to a certain village on a certain day to immunize, or it was communicating to Lagos, to the site we needed certain ped-o-jet parts, because, you know, 10 of our guns are down, and we really need these for the next campaign, and the rainy season is coming, and we need them tout suite, you know, right away (Diallo, 2006).

Dr. Ralph Henderson, who served as CDC’s Deputy Director of the West African Smallpox Program and later served as an Assistant Director General for the World Health Organization’s Expanded Immunization Program, described the troubles of getting Ped-O-Jet parts and the lack of supplies.

One of my problems as advisor was firing off cables about getting spare parts for the jet injectors. They kept running out of some tiny points-I didn’t know what they were, but I think that on a regular engine they’d be called the points. They relate to the electrical system. Forget it. But that’s all I knew. And I knew that they were burning out, and they couldn’t get spare parts. So one of my jobs as a technical advisor, very technical, was to send cables back saying, “Send more of these things because they can’t run the injectors.” Nor did CDC send enough diluent, so we were often using Evian, one of the French bottled waters, as diluent for the measles vaccine (Harden, 2006b).



These interviews give us several insights. For instance, we gain: 1) knowledge of what the CDC thought of jet injectors during the 1960s; 2) knowledge of how jet injectors were administered, and 3) knowledge about the performance of Ped-O-Jet injectors.

During the 1960s the CDC assumed the high velocity of the jet stream would not allow any cross-contamination. A common idea of the time that since there was no needle there was no risk. Although no safety test was conducted to confirm this assumption. As Dr. Foster stated, “At that time the question was the effectiveness of the Ped-o-Jet not the risk of infection.” However, as Jet Infectors has previously reported, the CDC first evaluated the safety of jet injectors in 1977 and found cross-contamination was possible.

The CDC researchers interviewed now admit there was no sterile technique when using the Ped-O-Jet. Bill Foege, the former Director of the CDC, acknowledged the Ped-O-Jet allowed for cross-contamination. Other interviews revealed vaccinators failed to sterilize the nozzle after accidentally dropping the Ped-O-Jet on the ground. Photographs captured vaccinators smoked cigarettes when performing inoculations and maintenance on the jet gun.

In numerous interviews are evidence that vaccinators used the Ped-O-Jet improperly. In one instance, a vaccinator held a jet gun in each hand, which means he failed to support the arm of the vaccinee and thus the injection was administered incorrectly. Several interviews reported vaccinators administered thousands of injections within a short time. Administering 600 jet injections in twenty minutes would mean an injection was given every two seconds (one second for the vaccination and another second for the next person in line to step-up). This demonstrates the vaccinator failed to hold the jet gun against patients’ arms for a full three seconds as per the manufacturer’s recommendation. In one instance, vaccinators used Evian water in the absence of diluent, yet the effectiveness of such an on-the-fly concoction was never previously tested.

The interviews also document numerous maintenance issues. Mr. Friedman noted the shoddy quality with which the Ped-O-Jets were made. The nozzle often became clogged and required being “reamed” out with a wire brush, thus potentially damaging the nozzle orifice. Moreover, the wearing of O-rings and the destruction of the aluminum foot-pedal demonstrate these Ped-O-Jet injectors were used beyond their intended life span.

Whether used within mass vaccination campaigns or within the United States military, Ped-O-Jets were assumed safe, administered by vaccinators with limited training, conducted in haste, at times improperly used, and faced frequent maintenance issues.


In no way is this article to assign blame to any of the CDC researchers interviewed, to the CDC in general or to the local volunteers who partook within the vaccination campaigns. At the time, knowledge of blood-borne pathogens was primitive. This article is purely to document how the Ped-O-Jet injectors were used and to gain a better understanding of what the CDC knew and thought of jet injectors throughout the 1960s and 1970s.



© Shaun Brown and 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.

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


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.


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