The challenges of worldwide vaccine roll-out are many and varied, with vaccine ‘hoarding’ by rich nations facing considerable criticism. Administration itself is a significant barrier – typically, patients must visit clinics, hospitals or vaccination centres, where a trained professional removes the vaccine from cold storage and injects it into the arm. Could that process be simplified?

Microneedle patches might be able to do just that. In development for more than 20 years, and now commercially available for some applications, the patches are covered in arrays of dozens of tiny points, which pierce the top layer of skin to deliver drugs. Generally produced through etching or moulding, the patches can be made of polymers, metals or even the drug being administered.

For those with a fear of needles, patches offer an anxiety-free way to protect health without the use of a hypodermic syringe. Microneedles minimise pain by only piercing the top layer of skin, avoiding deeper nerves. They can even be self-administered, cutting out a significant portion of the associated logistical challenges and enabling increased take-up.

Printed patches

Patches could even be more effective at stimulating an immune response than vaccines delivered by conventional needles, according to a team of researchers from Stanford University in California and the University of North Carolina, offering greater protection against viruses such as Covid-19.

Instead of conventional moulding, the team developed 3D-printed microneedle patches, built in a prototype printer invented by lead study author Joseph DeSimone. 3D printing enables easier customisation, said the team, aiding the development of patches for flu, measles, hepatitis or Covid-19.

Manufacturing hurdles

Conventional moulding is not very versatile, said the team, and the resulting microneedles sometimes lack sufficient sharpness to pierce the skin. Adapting microneedles for different vaccine types is another challenge, said fellow lead study author Shaomin Tian. “These issues, coupled with manufacturing challenges, have arguably held back the field of microneedles for vaccine delivery,” she said.

In animal testing, the researchers found that the vaccine patch generated a significant T-cell and antigen-specific antibody response that was 50 times greater than a subcutaneous injection. The heightened immune response could lead to ‘dose sparing’, they said, with a smaller dose generating a similar immune response to a vaccine delivered by needle.

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