**4. Conclusions and future prospects**

Since their first use as gene delivery vehicles, adenoviral vectors have been extensively studied in a number of applications and have improved substantially over time. Issues such as toxicity, pre-existing immunity in humans, and challenges in construction are continually being addressed. More recently, outbreaks of newly emerging infectious diseases, such as SARS, Ebola, and Zika, and the continuing threat of bioterrorism have increased the requirement of novel vaccine platforms which can be designed and produced in large scale within a short period of time. Adenoviral vectors, due to their versatility, ease of construction, adeptness to rapid mass production, and induction of robust transgene-specific humoral and cellular immune responses, have proven to be valuable in the development of vaccines for emerging viral infectious diseases. Furthermore, extensive knowledge about the adenoviral vector biology and the induced immune responses in animals have tremendously helped in developing effective vaccine candidates against several viral pathogens, which have progressed to advanced clinical stages. The adenoviruses are now at the forefront of vaccinology and have shown huge potential in both pre-clinical and clinical studies for HIV, malaria, Ebola virus, and Zika virus vaccines. Apart from infectious disease, adenoviral vectors have been approved for human use as cancer and gene therapy. Therefore, adenoviral vectors have opened new avenues in gene delivery, vaccine antigen delivery, and cancer molecular therapy.
