ABSTRACT
Vaccines are biologic preparations that elicit immune system responses that protect an animal against pathogenic organisms. The primary component of the vaccine is an antigen, which can be a weakened (attenuated) version of an infectious pathogen or a purified molecule derived from the pathogen. Upon oral administration or injection of a vaccine, the immune system generates humoral (antibody) and cellular (cytotoxic, or killer T cell) responses that destroy the antigen or antigen-infected cells. When properly administered, the immune response to a vaccine has a long-term memory component, which protects the host against future infections. Vaccines often contain adjuvants to enhance immune response, as well as formulation agents to preserve the antigen during storage or upon administration, to provide proper delivery of antigen, and to minimize side reactions.
