IMMUNIZATION | An Effective Therapy for Infectious Diseases

Immunization is a simple and effective way to protect us from infectious diseases

According to World Health Organization (WHO) Immunization is defined as the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body’s own immune system to protect the person against subsequent infection or disease. When you get an immunization, you're injected with a weakened form of (or a fragment of) a disease. This triggers your body's immune response, causing it to either produce antibodies to that particular ailment or induce other processes that enhance immunity. Then, if you're ever again exposed to the actual disease-causing organism, your immune system is prepared to fight the infection. Immunization is a proven tool for controlling and eliminating life-threatening infectious diseases and is estimated to avert between 2 and 3 million deaths each year.

Memory Action of the Immune System.

A key feature of the immune system is memory. Immunological memory is the ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response. Immunological memory occurs after a primary (first) immune response against the antigen. It is thus created by each individual, after a previous initial exposure, to a potentially dangerous agent. Memory is maintained by a subset of B and T lymphocytes called memory cells which can survive for years in the body. Memory cells remain ready to respond rapidly and efficiently to a subsequent encounter with a known pathogen, this is called secondary response. The course of secondary immune response is similar to primary immune response.

Immunological memory cells are responsible for creating secondary immune response

After the memory B cell recognizes the antigen, it presents the peptide: MHC II complex to nearby effector T cells. That leads to activation of these cells and rapid proliferation of cells. After the primary immune response has disappeared the effector cells of the immune response are eliminated. However, there remain antibodies previously created in the body that represent the humoral component of immunological memory and comprise an important defensive mechanism in subsequent infections. In addition to the formed antibodies in the body there remains a small number of memory T and B cells that make up the cellular component of the immunological memory. They stay in the body in a resting state and at the second or next encounter with the same antigen these cells are able to respond immediately and eliminate the antigen. Memory cells have a long life and last up to several decades in the body.

History of Immunization

Edward Jenner, a doctor in Berkeley in Gloucestershire, is known to be the founder of immunization. During the 18th century he established the procedure by introducing material from a cowpox vesicle on Sarah Nelmes, a diarymaid, into the arm of a boy named James Phipps. Edward Jenner noticed that some dairymaids seemed protected from smallpox if they had already been infected by the much less dangerous virus that caused cowpox.

Dr Jenner performing the first vaccination on James Philips

In 1796, Jenner conducted an experiment, scratching the arm of the 8-year-old boy, James Phipps using material from a cowpox sore in one of the dairymaids (Sarah Nelmes). Then he repeated the same experiment, but this time added a small amount of smallpox into the same child. He hoped that the procedure would immunize the child against the deadly smallpox infection. In fact, it did. Jenner’s experiment began the immunization age. The next major advance occurred almost 100 years later when Louis Pasteur, MD, showed that disease could be prevented by infecting humans with weakened germs. In 1885, Dr. Pasteur used a vaccine to successfully prevent rabies in a boy named Joseph Meister who had been bitten by a rabid dog. By the mid-20th century, regular progress in immunizations was made. Jonas Salk, MD, and Albert Sabin, MD, made what are perhaps the bestknown advances—they developed the inactivated polio vaccine and live polio vaccine, respectively. Their discoveries have saved countless children worldwide from polio, a disease that often left youngsters dependent on wheelchairs or crutches for life.

What is Immunization?

Immunization is defined as the procedure by which the body is prepared to fight against a specific disease. It is used to induce the immune resistance of the body to a specific disease. Immunization is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen). Immunization is of two types:

1. Passive immunization
2. Active immunization.

PASSIVE IMMUNIZATION

Passive immunization or immunity is produced without challenging the immune system of the body. It is done by administration of serum or gamma globulins from a person who is already immunized (affected by the disease) to a non-immune person. It is where pre-synthesized elements of the immune system are transferred to a person so that the body does not need to produce these elements itself. Passive immunization is acquired either naturally or artificially.

• Passive Natural Immunization
  Passive immunization occurs physiologically, when antibodies are transferred from mother to fetus during pregnancy, to protect the fetus before and shortly after birth. Before birth, immunity is transferred from mother to the fetus in the form of maternal antibodies (mainly IgG) through placenta. After birth, the antibodies (IgA) are transferred through breast milk. At this period the Lymphocytes of the child are not yet activated. In addition, the antibodies received from the mother are metabolized soon. Therefore, the passive immunity is short lived. The significance of passive immunity that is obtained before birth is the prevention of Rh incompatibility in pregnancy.

• Passive Artificial Immunization
  Passive artificial immunization is developed by injecting previously prepared antibodies using serum from humans or animals. Antibodies are obtained from the persons affected by the disease or from animals, particularly horses which have been immunized artificially. The serum containing the antibody (antiserum) is administered to people who have developed the disease (therapeutic). It is also used as a prophylactic measure. Prophylaxis refers to medical or public health procedures to prevent a disease in people who may be exposed to the disease in a later period.
  This type of immunity is useful for providing immediate protection against acute infections like tetanus, measles, diphtheria, etc. and for poisoning by insects, snakes and venom from other animals.

ACTIVE IMMUNIZATION

Active immunization or immunity is acquired by activating immune system of the body. Body develops resistance against disease by producing antibodies following the exposure to antigens. Active immunity is acquired either naturally or artificially.

• Active Natural Immunization
  Naturally acquired active immunity involves activation of immune system in the body to produce antibodies. It is achieved in both clinical and subclinical infections.

1. Clinical infection
   Clinical infection is defined as the invasion of the body tissues by pathogenic microorganisms which reproduce, multiply and cause disease by injuring the cells, secreting a toxin or antigen-antibody reaction. During infection, the plasma cells produce immunoglobulins to destroy the invading antigens. Later, due to the activity of memory cells, body retains the ability to produce the antibodies against the specific antigens invaded previously.
2. Subclinical infection
   Subclinical infection is defined as an infection in which symptoms are very mild and do not alert the affected subject. The disease thus produced may not be severe to develop any manifestations. However, it causes the activation of B lymphocytes, resulting in production of antibodies.

• Active Artificial Immunization
  Active artificial immunization is a type of immunization is achieved by the administration of vaccines or toxoids.

Vaccines
Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a pathogen. Vaccine is the substance that is introduced into the body to prevent the disease produced by certain pathogens. Vaccine consists of dead pathogens or live but attenuated (artificially weakened) organisms. The vaccine induces immunity against the pathogen, either by production of antibodies or by activation of T lymphocytes. Vaccination is the most effective method of preventing infectious diseases; widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the elimination of diseases such as polio, measles, mumps, poliomyelitis, tuberculosis, tetanus, rubella, yellow fever, rabies, typhoid, influenza, hepatitis B, etc. from much of the world.

Toxoids
Toxoid is a substance which is normally toxic and has been processed to destroy its toxicity but retains its capacity to induce antibody production by immune system. Toxoid consists of weakened components or toxins secreted by the pathogens. Toxoids are used to develop immunity against diseases like diphtheria, tetanus, cholera, etc. The active artificial immunity may be effective lifelong or for short period. It is effective lifelong against the diseases such as mumps, measles, smallpox, tuberculosis and yellow fever. It is effective only for short period against some diseases like cholera (about 6 months) and tetanus (about 1 year).

Summing up-Why Should Someone Get Immunized?

The goal of public health is to prevent disease. It's much easier and more cost-effective to prevent a disease than to treat it. That's exactly what immunizations aim to do. Immunizations protect us from serious diseases and also prevent the spread of those diseases to others. Over the years immunizations have thwarted epidemics of once common infectious diseases such as measles, mumps, and whooping cough. And because of immunizations we've seen the near eradication of others, such as polio and smallpox.

References

http://www.who.int/topics/immunization/en/
https://en.wikipedia.org/wiki/Immunization
https://www.webmd.com/children/vaccines/immunizations-vaccines-power-of-preparation
https://en.wikipedia.org/wiki/Vaccination
https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/History-of-Immunizations.aspx

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