5.2.1. Potential adjuvants
One of the salient features of an effective vaccine is the induction of protective antibody responses using the minimum dose of antigen so that it has the least requirement for repeated administration and assistance of immunostimulatory agents. In this way, many governments and even low-income countries globally will be able to order the new vaccine in a short time, since the cost of vaccine development will be affordable. Considering a suitable adjuvant in preparing SARS-CoV2 vaccine is recommended to achieve this grand affair [42]. So, adjuvants that stimulate remarkable antibody as well as cellular immune responses with approved safety and efficacy, such as rOv-ASP-1, CoVaccine HT, Matrix-M, delta inulin, MF59® and AS03 maybe be useful in accelerated vaccine candidate registration containing recombinant RBD or complete S proteins. Among the mentioned adjuvants, AS03, MF59®and also CpG 1018 have already received the necessary approvals for use in human vaccines, while the rest have shown promising results in clinical and pre-clinical trials. Protollin is the other novel adjuvant that stimulates general and mucosal immunity against respiratory viral infections and should be considered in SARS-CoV2 vaccine researches. Previous reports have indicated antibody-mediated disease exacerbation following the use of inactivated SARS-CoV and MERS-CoV vaccines with or without adjuvants. To date, however, there have been no similar reports of inactivated SARS-CoV2 vaccines and administering related vaccines with alum adjuvant in rhesus macaque host induced notable responses without disease aggravation. Nevertheless, Th1-assisted adjuvants can be used to solve this possible problem [42, 43].