The emergence of COVID-19 caused by SARS-CoV-2 in late 2019 precipitated an unprecedented global public health crisis, galvanising the scientific community to develop effective vaccines at record speed. Among the transformative outcomes of this pandemic response was the emergency use authorisation of the first-ever messenger RNA (mRNA)-based vaccines in humans—BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna)—within twelve months of viral sequence disclosure. BNT162b2 was co-developed by BioNTech, headquartered in Mainz, Germany, in partnership with Pfizer, making this a landmark achievement for European vaccinology. This review comprehensively examines the molecular biology of mRNA vaccine technology, including structural components, codon optimisation strategies, nucleoside modification approaches pioneered by Karikó and Weissman, and lipid nanoparticle delivery systems. We review the immunological mechanisms underlying mRNA vaccine-induced humoral and cellular immunity, analyse efficacy and safety data from pivotal Phase III trials, and discuss the limitations of the platform including cold chain requirements and durability of immune responses. Finally, we discuss emerging mRNA vaccine applications beyond COVID-19, positioning mRNA technology as a cornerstone of 21st-century vaccinology.
