Vaccine adjuvants: smart components to boost the immune system.

Vaccination is an effective approach to prevent the consequences of infectious diseases. Vaccines strengthen immunity and make individuals resistant to infections with pathogens. Although conventional vaccines are highly immunogenic, they are associated with some safety issues. Subunit vaccines are safe, but they require adjuvants to stimulate the immune system because of their weaker immunogenicity. Adjuvants are entities incorporated into vaccines to increase the immunogenic responses of antigens. They play a crucial role in increasing the potency and efficacy of vaccines. Different adjuvants have different modes of action; therefore, a better understanding of their immunology could provide guidance for the development of novel adjuvants. Numerous studies have been conducted using different types of adjuvants to characterize their potency and safety; however, in practice, only few are used in human or animal vaccines. This review aims to introduce the different modes of action of adjuvants and give insight into the types of adjuvants that possess the greatest potential for adjuvanticity.