A 3D-printed microneedle vaccine patch has been developed by scientists. Doses are applied to the skin - offering a pain-free alternative.
They can be stored for months at room temperature. It also opens the door to industrial sized shipments to developing countries.
Co-author Dr Ana Jaklenec, of Massachusetts Institute of Technology (MIT) in the US, said: "We could someday have on-demand vaccine production. If, for example, there was an Ebola outbreak in a particular region, one could ship a few of these printers there and vaccinate the people in that location."
The technique may revolutionise immunisation programs. A vaccine 'ink' is injected into moulds by a robotic arm. It is then sucked to the tips by a vacuum chamber. Patches - about the size of a thumbnail - contain hundreds of microneedles that enable the vaccine to dissolve.
Experiments found they were as effective at protecting mice against Covid-19 as traditional jabs. Most vaccines have to be refrigerated - making stockpiling and distribution difficult.
They also require syringes, needles and trained healthcare professionals to administer them. Similar patches are now in development to combat polio, measles and rubella. The tips of the needles dissolve under the skin - releasing the vaccine.
Lead author Dr John Daristotle said: "When Covid-19 started, concerns about vaccine stability and vaccine access motivated us to try to incorporate RNA vaccines into microneedle patches."
The 'ink' includes RNA vaccine molecules that are encapsulated in lipid nanoparticles - which help them remain stable for long periods. Once the moulds are filled, they take a day or two to dry. The current prototype can produce 100 patches in 48 hours.
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It's hoped future versions could be designed to have higher capacity. The researchers first created an ink containing RNA that encodes luciferase, a fluorescent protein.
They applied the resulting microneedle patches to mice after being stored at either 4 degrees Celsius or 25 degrees Celsius (room temperature) for up to six months. They also stored one batch of the particles at 37 degrees Celsius for one month.
Under all of these storage conditions, the patches induced a strong fluorescent response when applied to mice. In contrast, the fluorescent response produced by a traditional intramuscular injection of the fluorescent-protein-encoding RNA declined with longer storage times at room temperature. Then, the researchers tested their Covid-19 microneedle vaccine. They vaccinated mice with two doses of the vaccine, four weeks apart, then measured their antibody response to the virus.
Mice vaccinated with the microneedle patch had a similar response to mice vaccinated with a traditional, injected RNA vaccine. The researchers also saw the same strong antibody response when they vaccinated mice with microneedle patches that had been stored at room temperature for up to three months.
Professor Joseph DeSimone, of Stanford University in California who was not involved in the project, said: "This work is particularly exciting as it realises the ability to produce vaccines on demand. With the possibility of scaling up vaccine manufacturing and improved stability at higher temperatures, mobile vaccine printers can facilitate widespread access to RNA vaccines."
The researchers plan to adapt the process to produce other types of vaccines - including those made from proteins or inactivated viruses. Dr Jaklenec added: "The ink composition was key in stabilising mRNA vaccines, but the ink can contain various types of vaccines or even drugs, allowing for flexibility and modularity in what can be delivered using this microneedle platform."
The study was published in the journal Nature Biotechnology.
