**5. Recombinant vaccines/viral vectors**

Viral vector platform involves the insertion of the target gene that encodes for the target protein within an engineered. The viral vector can be able or disabled to replicate there are several viral vectors that are used in the recombinant vaccines such as vesicular stomatitis virus (VSV), adenovirus (Ad), measles virus (MV), alphaviruses, poxviruses, and herpes virus. These types permit the introduction of 5 kb the target gene and have been shown to induce cellular and humoral immunity. The possibility of preexisting immunity to viral vectors, such as Ad5 and MV in vaccine recipients, is one of the major concerns for this platform, which could reduce the vaccine's effectiveness [42]. To avoid this problem, methods such as selecting adenoviral serotypes with low human prevalence (Ad26 or Ad35) have been used.
