Types of vaccine and the immune response they induce

What it is

Vaccines are grouped by what part of the microorganism is used, and each group induces a different kind of immunity and a different need for a booster.

• Inactivated (killed): the microorganism is killed using heat or radiation, so there is no risk of developing the disease and the vaccine is safe. It induces a humoral immune response and needs a booster. Examples are IPV and rabies.
• Attenuated (live): attenuation comes from DNA mutation and long-term cell culture. It induces both cellular and humoral immune responses and needs no booster. Examples are MMR, OPV, Yellow Fever and BCG.
• Subunit: only part or a product of the microorganism is used, so only the antigenic fragment that stimulates the immune system is given. A booster is needed. An example is HBV.
• Conjugated: the outer coat of the microorganism, a polysaccharide and a poor immunogen, is conjugated to a highly immunogenic protein carrier. This induces a T-dependent response in the infant and creates an immunogenic vaccine, and no booster is needed. An example is Hib.
• Toxoid: the inactivated exotoxin of the microorganism is given, and the antibodies raised neutralize the toxic activity, giving high immunity. An example is DPT.