Critiquing CDC’s Review of the Literature

Within CDC’s 1986 investigation the administration conducted a review of the literature on jet injector safety. A review of the literature is a section within a paper that recognizes previous studies and articles that relate to the topic being investigated. The CDC’s review of the literature within their 1986 CDC report and also within their 1990 study stated the outcomes of jet injector studies. However, both failed to appropriately consider the limitations and differences of these studies. For instance:

  • British researcher H.M. Darlow found within his 1970 investigation, there was slight detection of radioactive labeled human serum on the nozzles of Port-O-Jet injectors. Despite the fact that he found contamination, he stated “icteric tragedies have been conspicuous by their absence,” meaning there lacked epidemiological evidence, at the time, to support the existence of a problem with hepatitis. Darlow assumed there was no real risk since recipients of the jet injector were not reporting any adverse health affects (Darlow, 1970). However, Darlow’s view does not account for the asymptomatic progression of serum hepatitis.
  • Black and colleagues (1978) found, after replicating Darlow’s experiment, no detection of radioactive human serum on the nozzle of a Med-E-Jet. Within the researchers in vitro investigation they administered injections into tissue infiltrated with radioactive isotope. The researchers concluded, “In the demonstrated absence of contamination with blood or tissue fluid, the risk of spreading hepatitis appears remote” (Black et al., 1978). Yet the 1985 outbreak by a Med-E-Jet injector has proven otherwise.
  • Abb, Deinhardt and Eisenberg (1981) found the injection sites and nozzle of a Ped-O- Jet were negative for Hepatitis B associated antigens after administering inoculations to two hepatitis B positive patients. However, Abb and colleagues rendered their opinion on a minuscule sample size. Moreover, the researchers failed to conduct the most critical test in determining cross-contamination by failing to test the ejected fluid for Hepatitis B antigens.
  • In 1985, Peter Brink and his colleagues studied the risk of virus transmission via jet injection. These researchers from the Netherlands assessed the degree of contamination after administering jet injections to mice chronically infected with lactic dehydrogenase (LDH) virus, a highly infectious pathogen. Results found 16 out of 49 (33%) mice became infected with the LDH virus after receiving injections from a Med- E-Jet injector. Most shockingly, researchers observed “post-injection bleeding was relatively uncommon,” occurring in only two out of 49 (4%) of the mice. Assuming the two bleeders were amongst the mice who became infected with LDH, indicates at least 14 out of 16 (88%) of the mice became infected despite the lack of visual bleeding. This is worth repeating, even though there was no visible bleeding during or after the jet injection, transmission of a highly infectious pathogen still occurred. This study demonstrates cross-contamination of highly infectious virus within microscopic levels via jet injection.
  • Brink and colleagues concluded transmission occurred when excessive tissue pressure after the the delivery/dispersion phase of injection caused retrograde flow of the liquid medicament that had mixed with skin tissues, blood, and the LDH virus. This retrograde flow is thought to be responsible for carrying the virus in the reverse path of the injection, out the injection site and contaminating the nozzle orifice of the jet injector. Brink stated until further investigations into the safety of jet injectors are conducted, “it might be justifiable to screen for HBsAg when a patient belongs to a high risk group, or to abandon the jet and give the treatment with individual syringes and needles” (Brink et al., 1985).
  • Brink and colleagues noted how several of the above investigations differentiated. Several studies—such as, Darlow (1970) and Abb and colleagues (1981) only delivered intracutaneous jet injections which were shallow injections and elicited less splash back. These studies used an intradermal nozzle, which acted as a spacer to achieve a shallower vaccination within the layers of tissue just under the skin. Therefore, these studies posed a lesser risk and produced negative to minimal contamination than deeper subcutaneous injections, as in Brink’s study, which required direct contact of the jet injector’s nozzle and the vaccinee’s skin. Brink had written, “the investigations cited above were designed to exclude the risk of transmission of virus infection by intracutaneous jet injections. However, subcutaneous jet injections might have a higher risk of contamination, because of the direct contact between skin and nozzle” (Brink et al., 1985).

Failing to note the above differences led readers to assume that the studies referenced were equivalent comparisons. As we have shown these studies were not comparable as they used an intradermal nozzle and were shallower injections which produced less splash-back.

Moreover, it is interesting to note that CDC’s review failed to mention the administration’s investigation of the Ped-O-Jet in 1977. It can not be said that the CDC didn’t know of its previous safety-testing conducted within the agency since Walter Bond, a CDC microbiologist, served in both investigations.


  • (Abb, Deinhardt & Eisenburg, 1981) Abb J, Deinhardt F, Eisenburg J. 1981 The risk of transmission of Hepatitis B virus using jet injection in inoculation. Journal of Infectious Diseases 144: 179.
  • (Black et al., 1978) Black J, Nagle CJ, Strachan CHL. Prophylactic low-dose heparin by jet injection.Br Med J 8 July 1978;2(6130):95.
  • (Brink et al., 1985) Brink PRG, van Loon AM, Trommelen JCM, Gribnau FWJ, Smale-Novakova IRO. Virus transmission bysubcutaneous jet injection. J Med Microbiol. December 1985; 20(3): 393-397.
  • (CDC, 1986) Centers of Disease Control. Epidemiologic Notes and Reports Hepatitis B Associated with Jet Gun Injection — California. MMWR 1986;35(23):373-376
  • (Darlow, 1970) Darlow HM. Jet vaccination. British Medical Journal 4(734):554, 1970.

© Jet Infectors, 2016 – 2021

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Revisiting Ismach’s 1959 Patent Reveals Ped-O-Jet was Unsterile

Aaron Ismach’s invention of the Automatic Jet Hypodermic Injection Apparatus, more commonly known as the Ped-O-Jet, attempted to overcome the risk of transferring hepatitis during mass immunizations. Although a review of his 1959 patent demonstrates the risk was not eliminated.

Patents contain an abundance of information. Amidst the detailed description about the uniqueness of the invention, a patent describes specific problems the invention intends to resolve.

Ismach proclaimed, “One of the outstanding benefits conferred by the invention in helping to prevent hepatitis or other cross-infection, is that if operation of the jet injection device is commenced in a sterile condition, the gun will maintain its own sterility” (Ismach, 1962).

Although this would also mean if the device failed to “maintain its own sterility” then it failed “to prevent hepatitis or other cross-infection.” This point is further upheld by Ismach stating, “the danger of cross-infection is almost completely avoided” (emphasis added) (Ismach, 1962). Ismach never declared the risk of cross-infection was completely avoided. He could not proclaim his own device was risk-free so he minimized the danger, as evidenced within this patent.

As the patent shows, Ismach believed the risk of transferring hepatitis was contingent upon whether the device became unsterile during the vaccination event.

Did the jet injector ever become unsterile? From Ismach’s patent, we can ascertain that yes, jet injectors, including his Ped-O-Jet device, were frequently unsterile.

Ismach claimed 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” (emphasis added) (Ismach, 1962).

Here Ismach subtly discloses that after the jet injector was fired there was fluid—whether splash-back of vaccine, blood, or tissue cells—upon the nozzle orifice. Any fluid upon the nozzle following an injection should have been recognized as contamination and thus the device was unsterile.
“Sucking fluid back…after the firing cycle” = Fluid Suck-Back
Ismach proclaimed that his invention was free from sucking fluid back after the firing cycle. He declared that failure to prevent fluid suck-back allows for “cross-infection” and states cross-infection is dangerous. Here Ismach was describing the undesirable phenomenon, so appropriately termed as fluid suck-back.

However, subsequent research has revealed the Ped-O-Jet was no exception to fluid suck-back.

  • The Department of Defense recognized the Ped-O-Jet was capable of sucking fluid back within a 1967 military specification. The specification alluded that conducting a performance test upon every Ped-O-Jet would remove any defective devices. “On cocking the gun, there shall be no drawback of fluid at the jet nozzle,” stated the specification (DoD, 1967; DoD, 1975). However, the performance test conducted was inadequate as it only evaluated fluid suck-back based upon a limited set of parameters and did not represent real life use of the device.
  • In 1977 researchers within the CDC’s Hepatitis Laboratories Division in Phoenix, Arizona, independently—and secretively—assessed the safety of Ped-O-Jet injectors. In their observations, a drop of fluid was observed on the nozzle orifice after firing an injection. “The drop would disappear (back into the injection nozzle head) in 3 to 5 seconds if the gun was held vertically or the drop would disappear immediately if the gun was cocked in a horizontal position” (CDC, 1977). These investigations represented real-life use of the Ped-O-Jet.

The CDC concluded that “disappearance of the fluid drop are common during clinical use of the jet injector” (CDC, 1977). Therefore fluid suck-back was not evidence of a defective device but of an inherent problem with the Ped-O-Jet in general.
“Sucking fluid back…during firing cycle” = Retrograde Flow
Ismach proclaimed that his invention was free of sucking flood back during the firing cycle. Ismach stated, there was “no danger of cross-infection, since nothing but the inoculating fluid itself penetrates beneath the skin of the patient” (Ismach, 1962). Yet the phenomenon of retrograde flow disproves this claim.

  • In October of 1998, the World Health Organization 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. A Ped-O-Jet device, renamed as the Am-O-Jet, was apart of this investigation. Hoffman found retrograde flow was a natural phenomenon within the jet injection process. Hoffman stated,

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).

Hoffman’s research revealed that despite the fact that there was no needle, there was transference of blood from the patient into the internal components of the jet injector. His research spotlighted the multidirectional flow between the patient and jet injector during the end of the injection process.
Ismach Knew Seriousness of Hepatitis
In 1959, Ismach was cognizant of the risk and seriousness of hepatitis. He knew that hepatitis could be transmitted by people who appear to have no symptoms. “It is possible for a patient to be a carrier of hepatitis and capable of seriously infecting another patient with the disease, although the carrier himself may show none of the symptoms associated with hepatitis” (Ismach, 1962).

Yet despite acknowledging the asymptomatic features of hepatitis Ismach minimized the risk of such transmission via jet injection. Remember Ismach stated, “the danger of cross-infection is almost completely avoided” (Ismach, 1962).
As Jet Infectors has shown throughout this review, the jet injector became contaminated in number of ways. Whether through contamination upon the nozzle orifice, fluid suck-back, or retrograde flow, it seems slight that this device ever remained sterile. Ismach’s claims to the safety of his invention do not carry any weight and amount to nothing more than puffing statements. The risk of transmitting Hepatitis B and Hepatitis C via jet injectors, including the Ped-O-Jet, is not merely theoretical or biological plausible but was in fact real.

  • (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).
  • (DoD, 1967) Department of Defense. Military specification: hypodermic injection apparatus, jet, automatic. Defense Supply Center, Phil-Troop Support / Medical Items of Supply. MIL-H-36505, 12 June 1967.
  • (DoD, 1975) Department of Defense. Military specification: hypodermic injection apparatus, jet, foot operated. Defense Supply Center, Phil-Troop Support / Medical Items of Supply. MIL-H-37084, 11 June 1975.
  • (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.
  • (Ismach, 1962) Ismach, Aaron. “Multi-dose jet injection device.” United States Patent 3,057,349. 9 October 1962. Accessible here.

© Jet Infectors, 2016 – 2021
Fair Use Notice (17 U.S.C. § 107)

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 – 2021

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. In his December 14th, 1959 patent, Ismach 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.

© Jet Infectors, 2016 – 2021
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?

© Jet Infectors, 2016 – 2021

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:
  • (Snowbeck, 2001) Snowbeck C. Reviving an old technology for large-scale vaccination. Post-Gazette. 20 November 2001. Accessible at:
  • (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 – 2021
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.

A researcher for the World Health Organization wrote about “reflux” when using Ped-O-Jets in his 1971 report on Yellow Fever vaccinations. Dr. Y. Robin noted,

The quantity of liquid expelled can be regulated from 0.1 to 1 ml. Owing to the reflux caused by the elasticity of the skin, in order to inject 0.10 ml it is necessary to eject 0.15 ml (Dull, 1968). This ejected volume was measured by weighing on a precision balance. The volume did not vary, throughout the operations, by more than +/- 5.3%, which is no greater than in the case of injection by syringe (WHO, 1971).

Here, Robin and Dull were noting the loss of vaccine during hole formation which occurred at the beginning of the jet injection. The use of the word “reflux,” meaning the backwards flow of a liquid, demonstrates that Robin and Dull both knew the vaccine flowed backwards. Granted these researchers did not know of the full effect of retrograde flow; however, Robin and Dull did state due to the elasticity of the skin the fluid was not absorbed within the body but moved backwards and out of the body.

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).

French researchers, du Châtelet and colleagues, acknowledged reflux of blood during jet injection. The researchers stated, “Transfer of virus from a chronic carrier to a healthy vaccinee through reflux of blood from the nozzle has been demonstrated, when vaccines are delivered in multi-dose vials” (du Châtelet et al., 1997).

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.

Even individual use, needle-free intradermal pens have shown in high speed cinematography to abide by retrograde flow. In their in-vitro studies, Rohilla and Marston (2019) observed

[A]t the conclusion of the dispersion stage, elastic stresses overcome inertial forces from the incoming jet stream and liquid in the bolus can flow back from the channel to the gelatin surface.

This high speed cinematography shows retrograde flow is not subject to one device or even a specific model of needle-free device but is a consistently occurring phenomenon when a liquid penetrates the skin at a high velocity.


  • (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.
  • (du Châtelet et al., 1997) Parent du Châtelet I, Lang J, Schlumberger M, Vidor E, Soula G, Genet A, Standaert SM, Saliou P, Imule Investigators Group. Clinical immunogenicity and tolerance studies of liquid vaccines delivered by jet-injector and a new single-use cartridge (Imule®): comparison with standard syringe injection. Vaccine 1997;15(4):449-458.
  • (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.
  • Rohilla P, Marston JO. In-vitro Studies of Jet Injections. Int J Pharm. 2019 Sep 10; 568: 118503.
  • (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, 1971) Robin, Y. Yellow Fever Vaccination, Alone or In Association, Using 17 D Vaccine Administered Intradermally. Geneva: World Health Organization, Expert Committee on Yellow Fever, document 2 March 1971; 1-5.
  • (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 – 2021
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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 – 2021

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).

  • By 1973, a scientific article had acknowledged the concern raised by previous researchers. The researcher, H.D. Wilson from a county health department in Scotland, even acknowledged that “during high-pressure injection, traces of blood may cover the inside of the bell [of the jet gun nozzle] adjacent to the skin, and the possibility of transfer of…hepatitis must be considered…” (Wilson, 1973).
  • Han and colleagues (2011) tried to overcome the threat of back splash with a needle-free micro jet injector. The researchers found,

A conventional drug jet may possess a volume in the range of 30 to 100 microliters, while the proposed microjet maintains a volume of a few hundreds of microliter, preventing back splash of interstitial liquid and delivering the same amount of drug by concentration change or multiple injections. This back splash is mainly caused by a large injected jet volume and is responsible for cross- contamination. (emphasis added) (Han et al., 2011)

To put this into perspective, the Ped-O-Jet manual lists the device can administer dosages between 0.1 cc to 1.0 cc, or rather 100 to 1000 microliters (Ped-O-Jet International, 1991). The average dosage for an immunization administered by a Ped- O-Jet within the DoD was 0.5 ml, or rather 500 microliters (DoD, 1970). As Han has reported, back splash was greater with larger injected volumes. The average dosage administered by a Ped-O-Jet was 500 times greater than dosages administered with the micro jet injector. The degree of backsplash would be greater allowing for cross- contamination.

  • Cu and colleagues (2020) observed splash back with a needle-free micro jet injection. The researchers used micro cinematography to capture a simulated jet injection. Within their paper, in figure 6a, bottom photo, “[T]he yellow circles show the back-splashes of the jet. The distance between the microfluidic device and the skin sample is 7.3 mm…” (Cu et al., 2020)
  • Portaro believed “enhancing the current knowledge of the fluid dynamics relating to jets penetrating human skin can help alleviate the problems associated with backsplash which leads to cross contamination among patients” (Portaro, 2013).
  • Yoh and colleagues (2016) noted the risk of cross-contamination from splash-back. The researchers also noted the specific parameters which need to be met to avoid splash-back.

Contrary to expectations, liquid jet injectors have the potential for cross- contamination from splash-back during injection if not high enough speed and not narrow enough jets are used, resulting in poor reliability of delivery dose and depth, and insignificant or no reduction in pain. (Yoh et al., 2016)

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.
  • (Cu et al., 2020) Cu K., Bansal R., Mitragotri S., Rivas DF. Delivery Strategies for Skin: Comparison of Nanoliter Jets, Needles and Topical Solutions. Annals of Biomedical Engineering, 48 (7); July (2020). pp. 2028-2039.
  • (DoD, 1970) Department of Defense. Immunization. TB MED 114; NAVMED P-5052-15A; AFB 161-9. By Order of the Secretaries of the Army, the Navy, and the Air Force. 25 May 1970. 33 pages
  • (Han et al., 2011) Han T., Han J., Yoh JJ. Drug injection into fat tissue with a laser based microjet injector. Journal of Applied Physics, 109, 093105 (2011).
  • (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.
  • (Ped-O-Jet International, 1991) Ped-O-Jet International. Instructions for the operation and maintenance of the Hypodermic Jet Injection Apparatus, Ped-O-Jet (foot operated) [Model POJ, NSN 6515-00-910-0097, rev. date 070191]. Cherry Hill, NJ 08002, USA.
  • (Portaro, 2013) Portaro R. Air-Powered Liquid Needle Free Injectors: Design, Modeling and Experimental Validation (thesis). Concordia University. February 2013.
  • (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.
  • (Wilson, 1973) Wilson HD. Experience of BCG Vaccination by Jet Injection in an Outbreak of Primary Tuberculosis. Lancet April, 28 1973; 1(7809):927-8.
  • (Yoh et al., 2016) Yoh JJ., Jang H., Park M., Han T., Hah J. A bio-ballistic micro-jet for !drug injection into animal skin using a Nd:YAG laser. Shock Waves 26, 39-43 (2016).

© Jet Infectors, 2016 – 2021
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.


© Jet Infectors, 2016 – 2021
Fair Use Notice (17 U.S.C. § 107)