Immunity and Vaccination: Key to Preventing Disease and Promoting Public Health

Immunity and vaccination are crucial aspects of our body’s defense against harmful infections caused by various pathogens. Understanding how our immune system recognizes and fights off foreign antigens helps us comprehend the importance of vaccination in preventing diseases and maintaining public health. Vaccines, containing weakened or inactivated pathogens, stimulate our immune system to develop immunity, providing protection against specific diseases.

Understanding Immunity and Vaccination

Immunity and its Mechanisms

• Immunity: It is the means by which the body recognises and resists infection resulting from the presence of specific foreign antigens on the surface of bacteria, viruses, fungi, or other toxins, chemicals, drugs or foreign objects, 
  • Example:  a splinter, which may be harmful. 
• Humoral Immunity (blood): It is activated by B lymphocytes, which produce antibodies (complement proteins, or cells that act on the microorganism associated with a specific disease, toxin, or foreign body). [UPSC 2022]
• Cellular Responses to Infective Antigens: 
  • T Lymphocyte Defense: The body also reacts to infective antigens with cellular responses, including those that directly defend against invading organisms and other cells which produce antibodies. 
    • T lymphocytes attack antigens directly and assist with chemicals controlling the immune response (cytokines). [UPSC 2022]
  • Inflammation: attracts white cells (macrophages and neutrophils), which act as phagocytes to kill germs and dead or damaged cells.

Terms in Immunology of Infectious Diseases

• Infectious agent: a pathogenic organism (e.g., virus, bacterium, rickettsia, fungus, protozoa, helminth, pollen, or chemical) is one capable of producing infection or infectious disease in humans.
• Infection: The process of entry, development, and proliferation of an infectious agent in the body tissue of a living organism overcoming the host’s defence mechanisms, resulting in a non-apparent or clinically manifest disease.
• Antigen: Any substance (e.g., protein, polysaccharide) which causes the immune system to produce antibodies against it. 
• Antibody: A protein molecule produced by the body’s immune system in response to a harmful foreign substance (an antigen) or acquired by passive transfer. 
  • Antibodies bind to the specific antigen that elicits their production, causing the infective agent to be susceptible to immune defence mechanisms against infections 
    • Example: Humoral and cellular. 
  • Antibodies may also form against one’s own tissue, producing an autoimmune disorder.
• Innate immunity: Includes the cough reflex, skin, mucus, and stomach acidity as barriers which protect the body against infection.
• Acquired immunity: It is developed as a result of natural exposure or deliberate exposure by immunisation to an infectious agent or its antigenic components, which protects against later exposure to the active live agent.
• Passive Immunity: The transfer of antibodies from one body to another provides passive immunity.
  • Maternal antibodies pass from mother to fetus through the placenta, offering protection during early life.
  • Antiserum or antitoxin containing antibodies from another individual provides short-term immunity against specific antigens.
  • Examples: include serum globulin for hepatitis infection and tetanus antiserum.
  • Passive immunity offers immediate protection but is temporary, as the transferred antibodies degrade over time.
• Immunoglobulins: Molecules produced by plasma cells in response to an antigen challenge and are present in blood or other body fluids. 
  • There are five major classes (IgG, IgM, IgA, IgD, and IgE) and subclasses based on molecular weight.
  • They can cross from a mother to a fetus in utero to provide passive immunity to the fetus.
• Antisera or Antitoxin: Materials prepared in animals for use in passive immunisation against infection or toxins.
• Cellular Immunity (cell-mediated immunity): Immunity acquired with T lymphocyte cells producing chemicals which activate natural killer cells (macrophages).
• Herd Immunity: Resistance of a group to an infectious disease when a large percentage of the population at risk is immune through previous exposure to the disease or by immunisation.
• Immunotherapy: It is a type of cancer treatment that helps your immune system fight cancer.
• Monoclonal Antibodies: These are antibodies (looking for a certain antigen) that have been generated artificially to help the body’s natural immune system. 
  • In the lab, monoclonal antibodies are made by exposing white blood cells to a specific antigen. 
  • To enhance the amount of antibodies produced, a single white blood cell is cloned, and identical copies of the antibodies are created.

Vaccination: Types and Mechanisms

• • Vaccine: It is a suspension of weakened, killed, or fragmented microorganisms or toxins or other biological preparations [such as those consisting of antibodies, lymphocytes, or messenger RNA (mRNA)] that is administered primarily to prevent disease. Vaccines may confer:
  • Active Immunity: against a specific harmful agent by stimulating the immune system to attack the agent. 
    • Once stimulated by a vaccine, the antibody-producing cells [called B cells (or B lymphocytes)] remain sensitised and ready to respond to the agent should it ever gain entry to the body.
  • Passive Immunity: by providing antibodies or lymphocytes already made by an animal or human donor.
  • Vaccines are usually administered by injection (parenteral administration), but some are given orally or even nasally (e.g. flu vaccine). 

• Various types of vaccines developed till now include:

• • Weakened or Attenuated Vaccines: These consist of microorganisms that have lost the ability to cause serious illness but retain the ability to stimulate immunity (may produce a mild or subclinical form of the disease). 
    • Attenuated vaccines include those for measles, mumps, polio (the Sabin vaccine), rubella, and tuberculosis. 
  • Inactivated vaccines: These are those that contain organisms that have been killed or inactivated. 
    • Inactivated vaccines elicit an immune response which is less complete than with attenuated vaccines; hence greater quantities of inactivated vaccines are administered. 
    • Vaccines against rabies, polio (the Salk vaccine), some forms of influenza, and cholera are made from inactivated microorganisms.
  • Subunit vaccine: It is made from proteins found on the surface of infectious agents. Toxins (the metabolic by-products of infectious organisms) are inactivated to form toxoids and used to stimulate immunity against tetanus, diphtheria, and whooping cough (pertussis).
• Recombinant DNA technology [UPSC 2021]: It has also proven useful in developing vaccines for viruses that cannot be grown successfully or that are inherently dangerous. 
  • Genetic material that codes for a desired antigen is inserted into the attenuated form of a large virus, such as the vaccinia virus, which carries the foreign genes ‘piggyback’. 
  • The altered virus is injected into an individual to stimulate antibody production to the foreign proteins and thus confer immunity. 
  • Vaccines against human papillomavirus (HPV) are made from viruslike particles (VLPs) prepared via recombinant technology.
• Naked DNA Therapy: It involves injecting DNA that encodes a foreign protein into muscle cells. 
  • The cells produce the foreign antigen, which stimulates an immune response.
• Messenger RNA Vaccine (mRNA vaccine): mRNA is a molecule that contains the instructions or recipe that directs the cells to make a protein using its natural machinery. 
  • To enter cells smoothly, mRNA travels within a protective bubble called a Lipid Nanoparticle. 
  • Once inside, our cells read the mRNA as a set of instructions, building proteins that match up with parts of the pathogen called antigens. 
  • The immune system sees these foreign antigens as invaders– dispatching defenders called antibodies and T-cells– and training the immune system for potential future attacks conferring immunity. 
  • GEMCOVAC-19 is India’s first home-grown mRNA Covid-19 vaccine.

Conclusion

• Immunity and vaccination are essential for preventing the spread of infectious diseases and maintaining public health.
• Through vaccination programs and advancements in vaccine technology, we can build immunity against various pathogens and reduce the burden of infectious diseases on individuals and communities.
• Investing in vaccination and public health infrastructure is crucial for achieving herd immunity and protecting vulnerable populations from preventable infections.

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