Vaccines are used to prevent diseases and improve immunity of the body. A vaccine is a biological preparation, contains an agent that resembles a disease-causing microorganism and is made from weakened and killed forms of microorganisms. Vaccines are categorized into many types. Some of the major types include inactivated vaccines, attenuated vaccines, toxoid and conjugate. Cholera, influenza, hepatitis A, polio and rabies vaccines are inactivated vaccines. Key attenuated vaccines are measles, mumps, rubella and typhoid.