In December 2019, a new contagious disease, later known as the coronavirus disease-2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first reported ^[1]. Since then, COVID-19 has rapidly spread across the globe, causing devastating medical, social, and economic consequences. In March 2020, the World Health Organisation (WHO) declared it a pandemic. There was a strong consensus that reliable vaccines are the most promising strategy to control the pandemic. Within a year after the disease outbreak, two messenger ribonucleic acid (mRNA) based vaccines became the first two vaccines to gain Emergency Use Authorisation (EUA) from the U.S. Food and Drug Administration (FDA), bringing hope to billions of people on the planet. Two mRNA vaccines, BNT162b2 (Comirnaty^®) and mRNA-1273, developed by Pifzer/BioNTech and Moderna, respectively, set the milestone in scientific history as the first-ever approved mRNA vaccines and opened a new era of mRNA-based approaches to prevent various diseases ^[2][3][4]. Never before have vaccines been developed and distributed in such a short period of time. A few more mRNA-based vaccines have reached various clinical stages of development (Table 1).

The lightning-fast success of these mRNA vaccines are not only built on the extensive research in mRNA therapeutic application during the last decades, but also the major technical innovations in nanotechnology for intracellular delivery and advances in nanomedicine production. In this entry, we will first introduce the principles of the mRNA vaccines against COVID-19, followed by a detailed discussion on the roles of nanoparticles, in particular lipid nanoparticles (LNPs), in assisting the transportation of mRNA into the acting site of host cells to exert its effects. The manufacturing and storage requirements of these are also briefly outlined.