Final answer:
An adjuvant is a substance added to a vaccine to enhance the immune response. It can be a vaccine prepared from killed bacteria, live bacteria that have lost their virulence, or used at the discretion of the veterinarian and the client. Vaccines contain antigens that stimulate an immune response and are effective in preventing viral infections.
Step-by-step explanation:
An adjuvant is a substance added to a vaccine to enhance the immune response. It can be a vaccine prepared from killed bacteria, live bacteria that have lost their virulence but retained their ability to induce protective immunity, or it can be used at the discretion of the veterinarian and the client. The existing vaccines include live attenuated vaccines, inactivated vaccines, subunit vaccines, toxoid vaccines, and conjugate vaccines, all of which contain antigens that stimulate an immune response. Vaccines are an effective way of preventing viral infections and have led to a decline in morbidity and mortality associated with viral infections.