Immunotoxic substances such as mycotoxins are unsuspected players in the failure of vaccines to provoke a proper immune response. Vaccines are commonly used to prevent various pathogenic challenges of viral, bacterial, and protozoan origins that usually lead to diseases affecting health and performance of livestock. G. Raj Murugesan, Technical & Marketing Director and Erika Hendel, Swine Technical Manager at Biomin, give an insight into two major types of vaccines normally used in swine production and two different mechanisms involved in establishing an immune response.