Transdermal approaches to vaccinations in the COVID-19 pandemic era

The COVID-19 pandemic has necessitated rapid vaccine development for the control of the disease. Most vaccinations, including those currently approved for COVID-19 are administered intramuscularly and subcutaneously using hypodermic needles. However, there are several disadvantages including pain and fear of needlesticks, the need for two doses, the need for trained health care professionals for vaccine administration, and barriers to global distribution given the need for cold supply chain. Recently, transdermal techniques have been under investigation for vaccines including COVID-19. Microneedle array technology utilizes multiple microscopic projections from a plate which delivers a vaccine in the form of a patch placed on the skin, allowing for painless antigen delivery with improved immune response. In this review, we discuss challenges of existing vaccines and review the literature on the science behind transdermal vaccines including microneedles, current evidence of application in infectious diseases including COVID-19, and considerations for implementation and global access.