IMMUNOLOGY

Detailed explanation-1: -A vaccine is a biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins.

Detailed explanation-2: -Invasive bacteria such as Salmonella, Listeria, Yersinia, Shigella and Mycobacterium bovis BCG have been used as vaccine vectors, capable of mounting potent humoral and cellular immune responses. Since these are pathogenic bacteria they were attenuated to generate suitable non-pathogenic vaccine strains.

Detailed explanation-3: -A vaccine is a suspension of weakened, killed, or fragmented microorganisms or toxins or other biological preparation, such as those consisting of antibodies, lymphocytes, or mRNA, that is administered primarily to prevent disease.