TABLE 2.

Advantages, limitations and challenges associated with various transmucosal route vaccine delivery systems.

Types of transmucosal delivery system	Advantages	Limitations	Challenges	References
Oral transmucosal vaccine delivery systems	Easy and self-administration Several dosage forms options Bypass first pass metabolism Fast onset of action from mucosal site Provides protection to the vaccine from acidic environment in gut and digestive enzymes High target specificity Controlled release of vaccine Rapid absorption because of increase blood supply Increased patient compliance Excellent accessibility	Small surface area for absorption Dissolution problem in patients with dry mouth Unpalatable May not be suitable for vomiting and unconsciousness patients Rapid clearance of administered vaccine by saliva Vaccines should pass from the mucosal barrier to reach site of action Inconvenient for some patients Irritation of oral mucosa Small dose limit	Protecting biological drugs such as peptides and proteins from enzymatic degradation Developing drugs or delivery systems that overcome the permeability barrier Polymeric vaccine delivery by parentral route is invasive and painful Limited efficient drug delivery systems	Sankar et al. (2011) and Cho et al. (2021)
Intranasal vaccine delivery systems	Highly vascularised mucosa Easy accessibility Needle free vaccination site Faster onset of immune response Induction of cross-reactive antibodies Reduction in the number of vaccinations required Lower cost Nanopowder has increased stability and ability to target further into the nasal cavity	Variability in dosing Nasal obstruction/inflammation Special applicators are sometimes required for nanopowders limiting the ease and increasing the cost of administration	High mucociliary clearance Narrow nasal passage Complex nasal geometry Negatively charged nanoparticles not compatible with mucosal delivery	Yusuf and Kett (2017)