A vaccine is a biological agent that provides active acquired immunity to a particular disease. A vaccine typically contains a component that seems like a disease-causing microbe and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. Vector is an organism that transfers a pathogen from reservoir to host. Traditional approach of live-attenuated vaccine immunization has resulted in remarkable success in the reduction and control of infectious disease. But many pathogens remain less responsive to the traditional vaccine strategies. Therefore, more appropriate vaccine strategies are needed. Recent discovery on the field of viral molecular biology and genetics has provided the opportunity to use viruses as vaccine platforms and as potential anti-cancer agents. Now-a-days viral vectors are considered as an attractive to the traditional platforms.

An adjuvant is an ingredient of that helps create a stronger immune response in the human body.  In short, adjuvants help vaccines work more efficiently. Drug delivery refers to approaches, formulations, and techniques for administering a pharmaceutical compound in the body to safely achieve its desired therapeutic effect. Both the vectors, adjuvants and delivery system are important to get the safe action of a vaccine.