Table 2.

Limitation of vaccines based on bacterial OMVs

Parent bacteria	Limitation	Resolvent	References
STEC strain (O157:H7 serotype)	Efficiency restricted to O157:H7 serotype	multi-antigenicity vaccines need to be explored	85
S. Enteritidis	Slightly toxicity	Improved stratgies to reduce endotoxin activity	87
E. coli	verification of protection effects only in mice	Further evaluation on other species	93
Neisseria meningitidis	Short duration when immunization beyond the vaccine strain	Repeat immunization and adapt other components of vaccines to OMVs	91
Neisseria meningitis	the safety need to be considered because of potent immune response	Vaccination with aluminum hydroxide to ensure safety	95
V. cholerae	LPS endotoxicity and expensive production of OMVs	Recombinant OMVs to reduce endotoxicity and advanced methods on OMVs isolation	99

Abbreviations: STEC, Shiga toxin-producing Escherichia coli; OMVs, outer membrane vesicles; S. Enteritidis, Salmonella Enteritidis; E.coli, Escherichia coli; V. cholerae, Vibrio cholerae; LPS, lipopolysaccharide;