Exploring natural components in vaccine delivery systems: Types, routes of administration, in-vitro and in-vivo quantification techniques

Vaccines are complex biopharmaceutical entities with the potential to enhance immune responses but also possess the risks of unintended immunogenicity or toxicity. However, delivering vaccines to the target site is challenging due to its stability and shelf-life issues. Different naturally obtained biodegradable polymers are recognized to overcome these limitations due to their fascinating characteristics, such as biodegradability, non-immunogenicity biocompatibility, and limited toxicity. Inappropriate bioavailability is always the major hurdle for the oral delivery of drugs and vaccines due to their low solubility and susceptibility to acidic environments. This review discusses the recent applications and prospective scopes of naturally obtaining polymers, such as poly (lactic acid-co-glycolic acid), alginate, chitosan, etc., in designing safe and effective vaccine delivery carriers. Further, this review highlighted the impact of carriers and routes on the immunization of vaccines. Besides, current work has underscored the recent advances in pharmacokinetics and pharmacodynamic techniques for quantifying vaccines, including in-vitro and in-vivo methods, with their challenges. Most significantly, this article emphasized clinical methods such as phase I-III clinical trials, immunogenicity assays, pharmacokinetic studies, and real-world effectiveness evaluation of vaccines. This work has also discussed the importance of cellular endosomal trafficking and the progress made in understanding vaccine toxicity studies.