Developing traditional viral vaccines for infectious diseases usually takes years, as these are usually produced either by chemical inactivation of the virus or attenuation of the pathogen, processes that can take considerable time to validate and also require the live pathogen. With the advent of nucleic-acid vaccines (DNA and mRNA), the time to vaccine design and production is considerably shortened, since once the platform has been established, all that is required is the sequence of the antigen gene, its synthesis and insertion into an appropriate expression vector; importantly, no infectious virus is required. mRNA vaccines have some advantages over DNA vaccines, such as expression in non-dividing cells and the absence of the perceived risk of integration into host genome. Also, generally lower doses are required to induce the immune response. Based on experience in recent clinical trials, mRNA-based vaccines are a promising novel platform that might be useful for the development of vaccines against emerging pandemic infectious diseases. This chapter discusses some of the specific issues that mRNA vaccines raise with respect to production, quality, safety and efficacy, and how they have been addressed so as to allow their evaluation in clinical trials.
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