The Development of Genetically Defined Live Bacterial Vaccines
It has long been recognised that vaccination with live organisms can induce more effective protection against infectious diseases than the use of dead vaccines presented in conjunction with currently available adjuvants. Live vaccines offer particular advantages in their ability to induce cell-mediated immune responses which are often critical for the establishment of solid protection against certain infectious agents. The route of vaccine delivery is also of importance. Oral vaccines can induce immune responses at mucosal surfaces and such responses are often lacking in individuals who receive parenteral vaccines. The combination of live organisms with oral delivery thus offers potential advantages for creating practical and efficacious vaccines. Many problems were experienced with early live vaccines because of the frequent occurrence of reversion to virulence and batch to batch variation. These problems were difficult to deal with because the attenuating lesions present in avirulent vaccine strains derived from virulent pathogens were uncharacterised at the genetic level. Recent advances in our understanding of the genetics and the mechanisms employed by pathogens to establish infections in the host has allowed the construction of genetically defined attenuated derivatives of many pathogens.
KeywordsVaccine Strain Live Vaccine Yersinia Enterocolitica Bordetella Pertussis Tetanus Toxin
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