Vaccines are of following types: 
Toxoids:

• Certain organisms such as diphtheria and Tetanus bacilli produce toxins.
  
• The toxins produced by these organisms are detoxicated and are used in the preparation of vaccines. e.g., diphtheria toxoid and tetanus toxoid. 
  
• These vaccines provide passive immunity for short period.

Live vaccines or attenuated vaccines:

• These vaccines are prepared from live (generally attenuated-the pathogen is made weakened to make it non-virulent) organisms.
  
• E.g.,-OPV, (Oral Polio Vaccine), BCG, (Bacillus Calmette Guerin), small pox, yellow fever, vaccine, influenza vaccine.
• These vaccines provide active life long immunity.

Killed vaccines or inactivated vaccines:

• Such vaccines are prepared by killing the pathogenic organisms by heat/ultraviolet rays/ alcohol/ formalin/ phenol.
  
• E.g., -Typhoid vaccine, Salk Polio Vaccine, Typhus Vaccine, Cholera Vaccine, Rabies Vaccine, Plague vaccine, TAB* vaccine

Combinations:

• If more than one kind of immunizing agent is included in the vaccine, it is called a mixed or combined vaccine.
• Some of the well known combinations are as follows: DPT (Diphtheria + Pertussis + Tetanus), DT (Diphtheria + Tetanus), DP (Diphtheria + Pertussis), Tetanus + Influenza, DPT and typhoid vaccine, MMR (Measles + Mumps + Rubella), Measles + Rubella.

Vaccines are also classified as follows:

First generation vaccines:

• These vaccines are developed by conventional technique using whole micro-organisms.
• They are never of uniform quality and produce side effects.

Second generation vaccines:

• These vaccines are produced by recombinant DNA technique/ genetic engineering. e.g., Hepatitis-B virus vaccine, herpes virus vaccine, pneumonia vaccine.
• The yeast derived recombinant hepatitis B virus vaccine is the first commercially available human vaccine, prepared by the genetic engineering technology.
• Thus, hepatitis B vaccine is produced from transgenic yeast by recombinant DNA technology.

• These are chemically synthesized multivalent vaccine.
• These Vaccines have high purity.
• eg, Vaccine against diphtheria toxin developed by Audibert et. at., 1981, leukemia virus vaccine.