There are many reasons that an eligible person might not receive a vaccine that is available to them. One such reason is a fear of needles, which can cause people to skip vaccinations and could therefore negatively affect their health. It is estimated that 1 in 4 adults has an extreme fear of needles. Fortunately for those individuals that fear current vaccination methods, a new much less painful approach may one day become the standard for vaccine delivery.
Microneedle vaccine patches have been in the news lately thanks to a recent development from scientists here at UNC and at Stanford. However, the idea to reform our vaccination strategies has existed long before now. In an article published in 2000 researchers described their own version of “transcutaneous immunization,” meaning a vaccine delivered within the layers of our skin.
Over the years, this delivery method has been proposed for a variety of illnesses such as the common flu, Measles, and more recently COVID-19. In 2015 researchers at Emory University and the Georgia Institute of Technology performed a clinical trial to test vaccine patches for the flu vaccine. Study participants were either given a traditional vaccine using a hypodermic needle or they received the vaccine via self-administered or healthcare provider administered vaccine patch. The study found that there was no significant difference in immune response between those who self-administered the vaccine and those who had a healthcare provider apply the patch. Immune response for the microneedle patch was similar to that of the traditional needle vaccine and both vaccine types worked better than the non-vaccine control. Most study participants preferred the patch over vaccination with a needle. Traditional vaccines using hypodermic needles must be administered by a healthcare provider forcing people to set up a vaccination appointment and take time out of their busy schedules to get a vaccine. However, as this study showed, vaccine patches can be administered by either a healthcare professional or the individual themselves. This removes the need to schedule an appointment making it easier and more efficient to obtain a vaccine which could boost vaccination rates.
Microneedle patch vaccines can work with a variety of vaccine types, including subunit vaccines. Subunit vaccines are a good option for vaccine development due to their increased safety over live attenuated and inactivated vaccines. Subunit vaccines are made of only certain parts of the virus causing them to have a decreased potency compared to vaccines that use a deactivated virus. Therefore, adjuvants are sometimes added to subunit vaccines in order to increase their effectiveness. The new microneedle vaccine patch developed by UNC and Stanford delivers subunit vaccines with adjuvants directly into the skin, known as intradermal vaccination. This type of vaccine delivery is advantageous because the skin is full of immune cells. When the vaccine is delivered directly into the immune rich environment of the skin, a better immune response can be achieved than with traditional subcutaneous (below the skin) vaccine application, where immune cells are not as abundant.
Traditionally the microneedles on the patch have been made using a variety of techniques, including through the use of molds as templates. However, there are several limitations to this strategy, including loss of needle sharpness and limited needle shape/arrangement. For example, it is difficult to use conventional microfabrication techniques to layer needles of different sizes and lengths on the same patch and the needles are usually limited to a smooth cone/pyramid shape when using molds. The recently published patch out of UNC utilizes a 3D printing technique called continuous interface liquid production, allowing for the microneedles to take on a number of designs and be printed quickly. The team tested a new innovative faceted microneedle design which looks something like a cartoon pine tree. The ridges in this design increase the surface area which allows for a more generous coating of the vaccine.
The vaccine patch could also address several other important issues relating to vaccine availability. Many vaccines, especially in liquid form, need to be stored at very cold temperatures. For instance, the Pfizer-BioNTech COVID-19 vaccine must be transported at temperatures between -130 and -76 degrees Fahrenheit. If the vaccine thaws it could decrease its potency or even render it useless. In many parts of the world the infrastructure to store and transport vaccines is unreliable or nonexistent. Microneedle patches containing dry, non-perishable vaccine could eliminate the need for cold storage. Patches that do not need to be refrigerated could even be mailed to people making the yearly flu shot a lot more accessible. Globally the current cost for refrigeration of vaccines is more than $13 billion. Making the switch to vaccine patches which are stored at room temperature could drastically reduce this global expense.
Yet another risk associated with traditional needle delivery is injury due to improper use or disposal of needles. For instance, hypodermic needles need to be disposed of in special containers specifically for “sharps” so that they do not injure anyone who might come into contact with regular garbage. Vaccine patches, on the other hand, feature microneedles which are applied directly to the skin like a bandage. The therapeutic then dissolves off of the microneedles or the microneedles themselves dissolve into the skin. Either way, the size and functionality of these patches eliminates the risk of needle injury and what remains of the patch can be disposed of in normal trash.
Microneedle vaccine patches applied directly to the skin present numerous advantages over traditional subcutaneous injections with hypodermic needles. With promising vaccine patch candidates for the flu and COVID-19, it’s possible that vaccine patches could soon become the standard vaccination method.
Header photo depicts microneedles used in vaccine patches. The image was taken using a scanning electron microscope. Credits: Peter DeMuth on the Medical Research Council’s Biomedical Picture of the Day.
Peer edited by Lacey Lopez and Taylor Tibbs