Vaccines are biological preparations which gives improved immunity to any specific disease. The immunity achieved by a vaccine is a type of artificial active immunity. An active immunity is achieved by introduction or exposure to small doses of the infecting microorganism. Active immunity can either be acquired naturally by sub-clinical infection, which are not usually noticed outside, or the immunity can be achieved artificially by the use of vaccines. The outside agent that is introduced into the body stimulates the body's immune mechanism to recognize the agent as a foreign body or antigen and produces antibodies, which destroys it. The body immune system recognizes and remembers that organism of infection and fights any infection that occurs in the future by that same organism. Vaccines are used prophylactically to improve the body's immunity and resistance against diseases.
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The characteristics of immunity produced by a vaccine is that the immunity produced is induced by an immunogen or agent. The immune response produced is durable and effective, although there is a lag period for its activation. The immunological memory is present in the body and subsequent immunity can be further achieved by booster doses of the vaccines given.
A vaccine is made up of a constituent or an agent that resembles the microorganism that causes that particular disease. Vaccines are prepared by attenuation of the microorganism called as the live attenuated vaccine and by killing the organism called as the killed vaccine.
Types of Vaccine:
1. Live attenuated vaccine. Some vaccines contain live attenuated form of microorganisms. Many of these vaccines are prepared by conditions that disable their virulent properties, which becomes less dangerous and produces a broad immune response in the body. The attenuation of live vaccine is done by techniques like aging of culture, cultivation at high temperature, continued cultivation, passage through different species, repeated subculture etc. Live attenuated vaccines can be prepared for both bacterial and viral diseases.
Bacterial vaccines. eg: BCG, plague, anthrax, brucella vaccines.
Viral vaccines. eg: Sabin polio vaccine, small pox, measles, influenza, mumps etc.
2. Killed vaccine. In killed vaccines, the microorganisms that were previously virulent were killed or destroyed by chemicals, heat, radioactivity, or antibiotics. Agents used to kill include formalin, phenol, alcohol, N-merthiolate, heat, ultraviolet light, photodynamic inactivation etc using appropriate techniques. Killed vaccines are available for both bacteria and viruses.
Bacterial vaccines eg: Cholera vaccine, TAB in enteric fever, and autovaccine.
Viral vaccines. eg: Influenza, rabies, Salk polio vaccine.
3. Bacterial products or toxoids. Toxoid vaccines are prepared by inactivated toxic compounds that cause illness. The inactivated toxoids are used to prepare the vaccines. Toxoid vaccines are effective in producing good immunity.
eg: Toxoids for diphtheria and tetanus.
4. Sub-unit vaccine. The protein sub-unit of the microorganism is used to prepare the vaccine instead of the whole organism. The sub-unit of the microorganism is capable of creating an immune response.
eg: Hepatitis B vaccine from surface proteins of the virus, human papilloma virus vaccine from the virus-like particle, influenza vaccine from the hemagglutinin and neuraminidase subunits, etc.
5. Conjugate vaccine. Some protein polysacharide outer coats of microorganisms are linked to toxic proteins can produce an immune response that can be recognized by the body.
eg: Haemophilus influenzae type B vaccine.
The Rare Drawbacks of Vaccine:
1. Vaccines do not guarantee complete protection from the disease.
2. Immunodeficient individual, where host's immune system does not respond adequately with the vaccine due to lowered immunity due to conditions such as diabetes, HIV infection, steroid use, age, etc.
3. Conditions where the host's immune system does not have the B cells capable of generating antibodies to the antigen.
4. Efficacy of the vaccine differs from one type of vaccine to other, depending on factors such as the type of disease, strain of vaccine, time of vaccine administration, nonresponders, ethnicy, age, and genetic predisposition.
5. The immunity develops only after a lag period.
6. Booster doses required for long term coverage.
Overall Benefits of Vaccine:
1. Vaccine helps to produce antibodies in large number of people that has helped in providing lifelong immunity from diseases.
2. A routine vaccination schedule has helped to get rid of some of the deadliest diseases that affected man on this planet.
3. Those diseases that have caused a great deal of suffering, disabling conditions, and death have now been controlled and eradicated with the help of vaccines.
4. Vaccination programs done worldwide has helped to bring down the mortality rate in many countries and improved the living conditions of people.
