Fish Diseases and Management

7.3.7.Characteristics of vaccines

Safety

A vaccine must simulate natural infection in producing the immune response but not the clinical disease. Killed or inactivated vaccines are safer than live ones but may have side effects. Live vaccines on the other hand may mutate and cause reversion of the pathogenicity and may cause from the disease.

Immunogenicity

Poor immunogenicity in the host, especially of the antigens associated with virulence, may be an adaptation of the pathogen to avoid the immune system of the animal. Attachment to immunogenic carriers like proteins or adsorption to adjuvants can improve the immunogenicity

Stimulation of protective immunity

Vaccine must include protective antigen and should induce immune response to virulence factors of the pathogen. Hence the final efficacy of the vaccines has to be determined after animal trials to see whether the vaccines are capable of inducing protective immunity to the animals. Serum antibody levels following the vaccination alone may not give any indication of immunity unless they are directed against protective antigens. It should be noted that in vitro cultures may be deficient in protective antigens.

Efficacy of Vaccines

Efficacy of any vaccine depends upon specificity and duration of protection offered by a particular formulation against a specific disease. In fish, duration of 1 year or life long protection can said to be commercially effective for any vaccine preparation.

Specificity

The vaccine should produce protection levels involving a memory component. This would mean that the vaccinated fish would be able to respond to the specific infectious agent in higher magnitude during the secondary response. In many cases, vaccines stimulate non-specific defence mechanisms, which provide non-specific protection for a short period – reducing the value of the challenge systems. Vaccine should not provide protection against unrelated pathogens. This would indicate lack of specificity and lack of memory