VACCINATION AND IMMUNISATION - Basic Biological Concepts for NEET

 

VACCINATION AND IMMUNISATION

What is Vaccine?

The process of introducing a vaccine in the body to develop immunity against a particular disease is called vaccination. The vaccine can be introduced in the body mostly by injection and sometimes orally, e.g., polio drops. Immunization provides immunity without infection through the introduction of weakened or killed antigenic pathogen or its toxoid into a healthy person. Immunity develops due to formation of memory cells by the cells of immune system. When a vaccinated person is infected by a pathogen, the existing memory T- or B-cells recognize the antigen and induce a massive formation of T-cells , B-cells and antibodies for eliminating the invader.

Types of Vaccines

A.     Based on Mode of preparation

1.      Live Vaccines or Attenuated Vaccines: Live Vaccines are prepared from live, weakened or nonvirulent organisms:
Examples: Vaccines for Measles, Mumps, Typhoid, OPV (Oral Polio Vaccine), BCG (Bacillus Calmette Guerin), Smallpox, Influenza, etc. these vaccines provide active life long immunity.

2.      Vaccines from Killed Germs: These Vaccines are prepared by killing the pathogenic organisms by heat/ ultraviolet rays/ alcohol/ phenol.
Examples: TAB (Paratyphoid A and Paratyphoid B vaccines), Vaccines for Plague, Rabies, Cholera, Typhus, Typhoid, Salk Polio vaccine, etc.

3.      Toxoids: Certain organisms such as bacilli of diphtheria and tetanus produce toxins. The toxins secreted by these bacteria are made harmless by treating them with formaldehyde. Formaldehyde denatures the proteins yet they retain the capacity to produce antitoxins.
Examples: Diphtheria toxoid and Tetanus toxoid. These vaccines provide passive immunity for a short period of time.

4.      Cellular Fractures: Extracted cellular fractions are also used in preparing vaccines.
Examples: Pneumococcal vaccines from polysaccharide contained in the capsule of the organisms, Hepatitis B polypeptide vaccines and Meningococcal vaccine from polysaccharide antigen from the cell wall.

5.      In combinations: In this case, more than one immunity vaccines are included.
Examples: DPT (Diphtheria + Pertussis + Tetanus), DT (Diphtheria + Tetanus), DP (Diphtheria + Pertussis), MMR (Measles + Mumps + Rubella).

B.     Based on the Method of Preparation: On this basis, vaccines are classified as follows:

1.      First Generation Vaccines: These vaccines are produced by conventional technique using whole microorganisms. These are attenuated live vaccine, killed or inactivated vaccines and toxoids.

2.      Second generation vaccines: These vaccines are prepared by genetic engineering or recombinant DNA technology. For vaccination against viral diseases, viral particles are genetically changed by adding or removing the genes so that they are not able to cause the disease but form the antibodies for that disease. Likewise, toxins and toxoids can be used as vaccines.
Example: Hepatitis-B virus vaccines, Herpes virus vaccine, Pneumonia vaccine. The first commercially available human vaccine produced by genetic engineering or recombinant technology is Hepatitis-B virus vaccine.

3.      Third Generation Vaccines (Synthetic Vaccines): These are chemically synthesized vaccines. These are purest in form and are of high potency.
Examples: Vaccine against Diphtheria toxin and Leukemia virus. Vaccination takes some time to react. Therefore, for a quick treatment against toxins, poisons or snake venom, performed antibodies, antitoxins and antivenins are injected to the patients. Such vaccines have been found very useful in case of tetanus and snake bite.