Table 2 Limitation of vaccines based on bacterial OMVs

Efficiency restricted to O157:H7 serotype

multi-antigenicity vaccines need to be explored

Slightly toxicity

Improved stratgies to reduce endotoxin activity

verification of protection effects only in mice

Further evaluation on other species

Short duration when immunization beyond the vaccine strain

Repeat immunization and adapt other components of vaccines to OMVs

the safety need to be considered because of potent immune response

Vaccination with aluminum hydroxide to ensure safety

LPS endotoxicity and expensive production of OMVs

Recombinant OMVs to reduce endotoxicity and advanced methods on OMVs isolation