In this essay we will discuss about the process of vaccination and immunisation in humans.
Vaccination is the most important method of preventing infection of micro-organisms, especially of bacteria and viruses. In this, a vaccine (antigen) is inoculated inside body to stimulate the formation of antibodies by the defensive system of the body, so a vaccine has antibody-provoking agents. Thus vaccination is “a preventive inoculation” as it protects a person from attack of pathogenic micro-organisms without the occurrence of disease. So a vaccine mimics the microbe we want to vaccinate against. Each vaccine provides a disease – specific means of prevention.
In this, the antigenic substance of a vaccine generates the primary immune response of low intensity and the memory of B- and T-cells. When the vaccinated person is attacked by the same pathogen, the existing memory T or B-cells recognize the antigen quickly and produce large number of lymphocytes and antibodies called secondary immune response of high intensity. So the principle of immunization by vaccination is based on the property of “memory” of the immune system.
This method of use of a vaccine for the treatment of a disease is called vaccinotherapy. The immunity developed may be temporary (e.g., cholera vaccine- immunity lasts for about 6 months) or permanent e.g., vaccine against smallpox, whooping cough, diphtheria and typhoid; or toxoids (toxins with antigenic property but with no toxic property) e.g., for tetanus; or attenuated live pathogens e.g., OPV, BCG and MMR (Mumps, Measels and Rubeolla) or antibodies against the pathogen e.g. ATS. Vaccination develops acquired immunity. Dead organisms or toxoids or attenuated live pathogens are no longer capable of causing disease but still have their chemical antigens.
The process of vaccination was first developed by Dr. Edward Jenner in 1796 A.D. He derived the word vaccine from Latin word vacca means ‘cow’. He found that milkmaids once attacked by a milder disease, cowpox, were immune to small pox. He confirmed his observations by experimenting on a healthy eight years old boy namely James Phipps on 14th May, 1796.
He first inoculated the boy with a cowpox pustule (a small in flamed area having pus) taken from a milkmaid, Sarah Nelmes. He noticed that boy suffered from a mild infection of cowpox and recovered. Dr. Jenner then inoculated the boy with material from a smallpox pustule from an infected person. Jenner observed that the boy did not developed smallpox even after a number of inoculations of smallpox pustule.
He concluded that the boy must have developed the immunity against the smallpox. This led to the discovery of smallpox vaccine later, it was Louis Pasteur (1885 AD), who discovered the vaccine against rabies or hydrophobia and called Pasteur treatment. He also discovered vaccine for anthrax and chicken cholera.
He found that ageing culture of cholera bacteria were too weak to cause disease when injected into the chickens. But chickens injected with these cultures became immune to fowl-cholera (Fig 8.13). In some, 2 or 3 additional doses, called booster doses, are given to produce immunity e.g. Polio.
Now, vaccines are available against the diseases like typhoid (TAB-vaccine), hiberculosis (BCG—developed by Calmette and Guerin), tetanus, cholera, smallpox (developed by Edward Jenner), diphtheria, polio (developed by Jonas Salk), measles (developed by Enders), whooping cough etc. In India, vaccines are generally produced at Hoffkins Institute at Mumbai and Virus Institute at Pune.
But no vaccine is yet available against malaria, trypanosomiasis etc. The vaccines produced by conventional methods from activated pathogens or live but weakened pathogens are called first generation vaccines. These have side effects on the body tissues. The vaccines produced by recombinant DNA techniques are called second generation vaccine e.g. Hepatitis-B vaccine has been produced from yeast by recombinant.
DNA technology and acts against hepatitis-B virus which causes jaundice and liver cancer. It has been produced from the transgenic yeast.
Now a day, synthetic vaccines, called third generation vaccines, have been introduced. These vaccines have been included in the immunisation programmes which have enabled to completely radical the deadly disease small pox, while have enormously decreased the frequency of many other diseases like polio, pneumonia, tetanus, diphtheria, etc.