The Needless injections, a brief description

A jet injector is a type of medical injecting syringe that uses a high-pressure narrow jet of the injection liquid instead of a hypodermic needle to penetrate the epidermis. It is powered by compressed air or gas, either by a pressure hose from a large cylinder, or from a built-in gas cartridge or small cylinder. Jet injectors are used for mass vaccination, and as an alternative to needle syringes for diabetics to inject insulin. As well as health uses, similar devices are used in other industries to inject grease or other fluid.
The Jet Injector Gun and the Ped-O-Jet are air-powered medical injector devices designed to administer vaccinations very efficiently. Invented by Aaron Ismach, these medical devices were bought in mass quantities by the US government and provided to governments around the world to eradicate smallpox and other diseases. Servicemen in the Armed Forces were routinely injected with these medical devices to immunize them, and civilian usage included vaccinations during situations such as flu epidemics. The Jet Injector is powered by electricity, while the Ped-O-Jet version is powered by a foot pump and does not require electricity to administer the vaccines. These devices have various specialized nozzles for different medication densities, and can also be used to inoculate animals. The Biojector 2000 is a make of gas-cartridge-powered jet injector. It is claimed that it can deliver intramuscular injections and subcutaneous injections up to 1 milliliter. The part which touches the patient's skin is single-use and can be replaced easily. It can be powered from a big compressed gas cylinder instead of gas cartridges. 

There have been relatively few incidents of disease transmission between users, despite widespread use of the jet injector by the military and in large-scale vaccination campaigns. Nevertheless, because the jet injector breaks the barrier of the skin, there is a potential that biological material is transferred from one user to the next. Some infectious viruses such as hepatitis B can be transmitted by less than one millionth of a milliliter so makers of injectors need to ensure there is no cross-contamination between applications. The World Health Organization no longer recommends jet injectors for vaccination due to risks of disease transmission. An experiment using mice, published in 1985, showed that jet injectors would frequently transmit the viral infection LDV from one mouse to another. Another study used the device on a calf, then tested the fluid remaining in the injector for blood. Every injector they tested had detectable blood in a quantity sufficient to pass on a virus such as hepatitis B.
From 1984-1985 a weight-loss clinic in Brazil injected a pregnancy hormone into their clients, mostly using a jet injector. It was noted that a number of these patients became sick with hepatitis. When studied, 57 out of 239 people who had received the jet injection tested positive for hepatitis B.
As well as transmission between patients, jet injectors have inoculated bacteria from the environment into users. In 1988 a podiatry clinic used a jet injector to deliver local anesthetic into patients' toes. Eight of these patients developed infections caused by Mycobacterium chelonae. The injector was stored in a container of water and disinfectant between use, but the organism grew in the container. This species of bacteria is sometimes found in tap water, and had been previously associated with infections from jet injectors. Despite the questionable hygiene transmission issue the idea of injector sprays has not been forgotten.

MIT has developed an injection system that uses a powerful magnetic piston to push a near-supersonic dose of medication straight through your skin into your body. The new jet injection method delivers a drug through the skin at speeds of up to 340 meters per second and in under a millisecond. The amount of drug can be varied, as can how deep it is injected. And as far as the patient is concerned, they shouldn’t feel anything other than the tip of the injector against their skin, because the jet is as thin as a mosquito’s proboscis.
By altering the intensity and duration of the injection pulse, the MIT hypo can deliver drugs in different dosages to different layers underneath the skin, allowing doctors to tune injections to give patients exactly what they need. This also means that doctors can use different injection strengths for infants and adults. Allowing the system to be programmable for delicate areas such as the surface of an eyeball or skin.
And lastly the Painless Laser Epidermal System (a.k.a. P.L.E.A.S.E.) device offers a painless and effective solution for drug delivery. Unlike the conventional methods, it operates creating micropores via laser ablation in the outer skin tissue up until the dermis where the nerves and blood vessels are and delivers the drug through pores. Since its UI is simple, both medical personnel or patients by themselves can use it. Recently acquired CE certification, you may expect to find it on the markets in Europe. Developed by Pantec Biosolutions, a private drug delivery company specialized in using laser microporation technology to deliver large molecular weight drugs into the epidermis for local or systemic uptake, offers a painless alternative. Although the system uses a disc infused with the medicine as one dose, it may seem wasteful but offers as a hygienically clean solution to the spread of germs in a multiple vaccination scenario. The laser used is a class 1 and is relatively safe, though laser safety protocols maybe put into practice. According to the website the Painless Laser Epidermal System is still under development.
It may be a long while before pain free injections as will be a reality, the jet injector seemed to be the next big thing at the time but proved to have a flaw in hygiene particularly in the spread of hepatitis B. Meanwhile MIT may think the idea of attaching a small rail gun to a plunger, it still needs testing particularly for cross contamination in multiple test subjects. Laser Epidermal System seems like a possible winner with each dosage cartridge acting as a barrier between skin and drug delivery system. Considering that the simple hypodermic syringe is a tried and tested method competing methods will need to be cost effective and  completely safe before wide spread usage. Testing and proper assessments will still be needed to be carried out for both systems, but eventually expect to see star trek technology at your general practitioner...