Squeamish patients who cannot stand the sight of needles could be offered pain-free injections, thanks to the work of Cardiff scientists.
The new micro-needles are long enough to penetrate the skin but not to reach pain receptors.
They were designed to introduce a DNA vaccination directly into skin cells.
They were revealed at the British Pharmaceutical Conference and developed at the Welsh School of Pharmacy at Cardiff University.
'Bed of nails'
The micro-needles, made by the Tyndall National Institute in Ireland, measure up to 300 microns (0.3mm) across, and are barely visible to the naked eye.
A tiny plate containing up to 400 needles is used and tests have found them to be completely painless.
James Birchall, head of the gene delivery research group, said: "Think of the bed of nails effect - the forces are spread over a wide surface area."
Dr Birchall said conventional needles went in too deep for the method of "genetic vaccination" his team was developing.
The micro-needles worked by creating temporary channels in the skin to allow the vaccine to reach "immune-responsive" skin layers, he said.
Cheap to make
They are currently made of silicon, but biodegradable needles that dissolve in the skin are a future possibility.
Dr Birchall said DNA vaccines delivered via a micro-needle could have several advantages over standard vaccines.
The new micro-needles are said to be completely pain-free
"They are likely to be cheaper and easier to make. The micro-needle system might also be developed as a patch for self-application, avoiding the need for a clinician," said Dr Birchall.
"There is also reduced risk of transmission of blood-borne pathogens by inappropriate re-use of needles. These are all particular advantages for the developing world.
"Pain-free vaccination could also be useful for childhood vaccines in developed countries."
The next stage of the research will investigate delivery of vaccines such as hepatitis B and influenza.
The new needles are not likely to be seen in hospitals or surgeries for at least five years.