Vaccination is deliberate introduction of the disease causing agent in some form (attenuated, killed and toxoid) in a healthy child, to incite a special response (known as immune response), which offers protection from contracting the full blown disease in future.

Types of Vaccines

Live attenuated vaccines: These vaccines are very potent and can provide long lasting protection against diseases. The vaccines contain live but weakened (attenuated) germs which have lost their capacity to cause illness but retain their ability to induce a protective response in the body. Common examples include OPV (oral polio vaccine), BCG and Measles vaccine.

Killed vaccines: These vaccines are relatively less potent and provide protection for a short duration. Therefore, frequent doses are required. The vaccines contain killed (by heat or chemicals) germs which still can induce a protective response in the body. Common examples include Pertussis, Rabies and killed typhoid vaccine.

Toxoids: A toxin that has been treated to destroy its toxicity, may still retain its ability to induce protective response (by anti-bodies). Such preparations are known as toxoid. Common examples include Tetanus and Diphtheria toxoids.

Other vaccines: These include polysaccharide vaccines (e.g. Pneumococcal vaccine) and conjugated vaccine (e.g. Hemophilus influenza B vaccine)

How do vaccines work?

The idea of introducing vaccines (that is live or killed germ particles) into the human body is to make  the body’s defence system believe that it is under attack by the bacteria or the virus. Our defence mechanism recognises this organism and start preparing for a fight by producing protective factors referred to as anti-bodies.

The first time such an interaction occurs, the body takes some time to identify the foreign organism and then produce anti-bodies but subsequently, the anti-body formation is quicker because the body tends to remember the offending organism and accordingly act faster. This process, known as immunological memory, enables the body to produce the same kind of anti-bodies more rapidly and in higher quantities on repeated contacts with the disease causing agent.