5.2. Vaccine platforms
Mostly, designed vaccines are divided into 6 categories based on their platform including inactivated or killed, live attenuated, DNA or RNA, protein subunit, engineered viral vector and virus-like particle (VLP). From a more generalized perspective, vaccines require two basic components: the antigen that is either provided by the vaccine or produced by the expression system of vaccinated individual, and the non-specific innate immune stimuli, which are mainly provided by alarmins such as damage-associated molecular pattern (DAMP) or pathogen associated molecular pattern (PAMP) molecules. The live attenuated vaccines are the only platform that deliver both necessaries intrinsically, while the other non-viral vaccine platforms require artificial alert molecules commonly known as adjuvants. Furthermore, the non-viral platforms depend primarily on multiple booster doses to provide desirable protection whereas the live attenuated vaccines usually make immunity after a single dose of administration [8]. Like the non-viral vaccines, the inactivated or killed platforms sometimes require adjuvant and multiple administration for effective immunization [41].