Needleless vaccines are attractive because they cause less pain and stress for people with needle phobias. But they have other advantages.
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Jet injectors and beyond
The first needleless injection systems date back to 1866 and used jet injectors. These hand-held devices used pressure to penetrate the skin and deliver drugs.
They became increasingly popular around the middle of the 20th century and were used to administer vaccines against typhus, polio, and smallpox.
A hepatitis B epidemic linked to their use led to their discontinuation in the 1980s. However, research resumed in the 1990s. Variants included a spring-loaded injector (a spring is released to deliver the drug), a battery powered jet injector and a gas powered jet injector.
Jet injection has also been used in dental care to deliver local anesthesia.
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Beyond jet injection, oral vaccines, including rotavirus, cholera, polio, and typhoid, have been around for several decades and are still used today in various parts of the world. They can be in liquid or tablet form.
More recently, researchers and biotech companies have developed vaccines that you inhale, such as nasal sprays, as well as skin patches. Most of these are still in the clinical trial phase.
DNA-based vaccines and gene gun
DNA vaccines were a fortuitous discovery following the first experiments with gene therapy in the 1990s, where injection of DNA into muscle unexpectedly generated an immune response.
With a DNA vaccine, a small part of the virus’s genetic material is introduced into cells under the skin. These cells then express DNA in the form of viral proteins. The body recognizes them as foreigners and stimulates an immune response.
DNA vaccines are simple and inexpensive to produce in large quantities, and they are relatively safe because they do not contain any infectious agents, such as a live virus.
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Scientists have explored a number of ways to deliver DNA vaccines, with a needle or without a needle. Needle-free methods include ultrasound (sound waves) and electroporation (electrical pulses) which disrupt cell membranes, allowing DNA to enter cells.
The gene gun or “biojector 2000”, a form of jet injector, appears to be the most efficient method. This uses pressure to inject DNA into the deep layers of the skin. Because it improves vaccine delivery deeper into the injection site, this method uses much less DNA than injection with a needle to generate the same immune response.
But no DNA vaccine has yet been licensed for use in humans. Although needleless DNA vaccines have been successful in preclinical and early clinical trials, DNA vaccines in general are also not as effective in generating immune responses against diseases such as HIV and cancer.
Needle-free COVID-19 candidates
The University of Sydney recently received federal government funding to begin human trials using a “liquid jet” injector to deliver their DNA vaccine.
Liquid jet injectors use small volumes of liquid forced through a small opening (smaller than a human hair). This ultra-fine high pressure flow penetrates the skin where the cells then take the vaccine and stimulate the immune cells.
This method has been effective in several clinical trials against HIV and is currently used to administer some influenza vaccines.
Other needle-free COVID-19 vaccines in development include a bandage-shaped patch made up of 400 tiny needles, a nasal vaccine, an oral vaccine in tablet form, and a needle-free device that delivers an mRNA vaccine.
MRNA-based vaccines work similarly to DNA vaccines.
Advantages and disadvantages
The advantages of needle-free vaccine technology, especially jet injectors, include:
- they can be much more acceptable to people who are afraid of needles, including children
- there is no risk of accidentally injuring yourself with a needle
they eliminate needle disposal (up to 500 million needles are thrown to the landfill each year after vaccinations, and 75 million of them could be infected with blood-borne diseases)
they improve the delivery of the vaccine to the skin and use a smaller vaccine volume.
The disadvantages include:
- start-up costs for those who use the device, including the purchase of guns and access to gas / air systems to fuel them
staff administering the vaccine will need special training and may not feel comfortable using the technology
the equipment requires regular maintenance.
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