Vaccination is one of the most efficient tools for disease prevention, and a continuously growing field of research. However, despite progress, we still need more efficient and cost-effective vaccines that would improve access to those in need. In this review, we will describe the status of virus-vectored vaccine technology with a focus on adenoviral-based vaccines. Adenovirus (Ad) vaccines have proven to be efficient in military vaccinations against Ad4 and Ad7 and as highly efficient vectored vaccines against rabies. The question of how other adenovirus-based vaccines can become as efficient as the rabies vaccine is the underlying theme in this review. Here, we will first give an overview of the basic properties of vectored vaccines, followed by an introduction to the characteristics of adenoviral vectors and previously tested modifications of the vector backbone and expression cassettes, with a focus on how they can contribute to increased vaccine cost-effectiveness. Finally, we will highlight a few successful examples of research that have attempted to improve the use of adenoviral-based vaccines by improving the transgene immunogenicity.