The global COVID-19 pandemic has brought tremendous momentum to the field of messenger RNA (mRNA) vaccines. The advantages of this vaccine platform, such as rapid development and high efficacy, resulted in mRNA vaccines being the first approved vaccines against COVID-19. Looking forward to the development of future vaccines, how can we make RNA vaccines even better? While improvements in the stability of the formulation and cost of the vaccine are inevitable, one of the main challenges is lowering the dose of RNA in order to avoid side effects associated with high doses of RNA. One way to do this is by using self-amplifying RNA (saRNA), a type of mRNA that encodes a replicase that copies the original strand of RNA once it’s in the cell. Here, we discuss the origins of saRNA, how it works in comparison to mRNA, current challenges in the field and the future of saRNA vaccines.