Active immunity is the resistance developed by an individual in response to an antigenic stimulus.
The antigen may gain entrance either by natural infection or through any other sources such as artificial immunization by vaccination.
a. Natural Active Immunity:
Immunity is developed by the host in response to the antigen that enters by natural infections. For example, a person attacked by measles or smallpox develops natural active immunity as he recovers from the diseases.
The immunity acquired by way of such infections is also long lasting in many cases. For example, lifetime immunity is got following certain viral infections such as smallpox, measles, and mumps.
b. Artificial Active Immunity:
In artificial active immunity, immunity is attained by the host in response to the antigen got by vaccination. Vaccines are preparations of live (attenuated) or killed microorganism or their products (toxoids).
- Live Vaccine (attenuated): in this preparation, live microorganisms are attenuated by different methods. Attenuation results in the loss of pathogenicity without the loss of antigenicity of the microorganisms.
E.g.: Anthrax vaccine, BCG (Bacille Calmette Guerin), Sabin Vaccine (oral Poliomyelities Vaccine), Measels Vaccine.
- Vaccines prepared with killed microorganisms: In this vaccines, microorganisms are killed in their virulent phase either by heat or antiseptics. While killing, care is taken not to denature the antigen by excessive heat or strong detergents.
E.g.: salk vaccine, Influenza vaccine, TAB vaccine, Pertussis vaccine, Toxoid, Tetanus Toxoid (TT), Diptheria Toxoid, Triple Vaccine (DPT).
Immunization schedule for Children
|From 3rd day after birth||BCG|
|3 months||DPT (1) OPV (1)|
|4 months||DPT (2) OPV (2)|
|5 months||DPT (3) OPV (3)|
|16 months||Booster dose or DPT and OPV|
- DPT = Diptheria, Pertussis, Tetanus vaccine (Triple vaccine)
- OPV = Oral polio vaccine