A Single-Administration Microneedle Skin Patch for Multi-Burst Release of Vaccine against SARS-CoV-2.

The necessity for multiple injections and cold-chain storage has contributed to suboptimal vaccine utilization, especially in pandemic situations. Thermally-stable and single-administration vaccines hold a great potential to revolutionize the global immunization process. Here, a new approach to thermally stabilize protein-based antigens is presented and a new high-throughput antigen-loading process is devised to create a single-administration, pulsatile-release microneedle (MN) patch which can deliver a recombinant SARS-CoV-2 S1-RBD protein-a model for the COVID-19 vaccine. Nearly 100% of the protein antigen could be stabilized at temperatures up to 100 °C for at least 1 h and at an average human body temperature (37 °C) for up to 4 months. Arrays of the stabilized S1-RBD formulations can be loaded into the MN shells via a single-alignment assembly step. The fabricated MNs are administered at a single time into the skin of rats and induce antibody response which could neutralize authentic SARS-CoV-2 viruses, providing similar immunogenic effect to that induced by multiple bolus injections of the same antigen stored in conventional cold-chain conditions. The MN system presented herein could offer the key solution to global immunization campaigns by avoiding low patient compliance, the requirement for cold-chain storage, and the need for multiple booster injections.