Recent Advances in Vaccine Technologies
Most vaccines that are available today rely on either inactivated (killed) or live attenuated (weakened) technologies. Such approaches have been successfully used to address many of the important veterinary and human diseases. However, both techniques have their limitations and associated potential problems.
Inactivated vaccines must be totally innocuous and noninfective. Problems with field outbreaks in the past have occasionally been attributed to incomplete inactivation. Such problems should not, and would not, exist if more reliable inactivants, inactivation procedures, and innocuity testing were used within the manufacturing process. Furthermore, because the manufacture of such vaccines involves the culture of large amounts of the infectious agent, there is a potential hazard to the personnel involved and the environment. Vaccines grown in eggs, tissue culture, or simply culture medium may contain unwanted “foreign” proteins, which could affect immunogenicity or be potentially allergenic/reactogenic. Finally, inactivated vaccines have certain limitations on their mode of presentation and as a consequence the nature of the immune response they can elicit. The response to vaccination may be limited and of short duration with adjuvants or immunostimulants required to enhance their overall immunogenicity/efficacy.
Attenuated vaccines must be precisely controlled and characterized in order to provide the required level of protective immunity without causing significant disease symptoms within the host animal. There is also a low risk that the attenuated antigen may revert to full virulence, and careful reversion to virulence safety studies must be carried out. Furthermore, in culturing the vaccine antigen, it is possible that other infectious agents may be introduced that could themselves lead to undesired side effects when the vaccine is used in the field.
Because of these and other reasons, including protective efficacy, economy of manufacture, and whether the infectious agent can be produced in vitro, scientists have turned their attention more and more to the new vaccine technologies. These vaccine technologies include split-product, subunit, isolated protein, peptide, marker vaccine, live vector, and nucleic acid approaches.