The concept of immunization is rooted in the historical work of pioneers and the body’s natural and acquired immune responses.

• Historical Basis: Edward Jenner (1749-1823) discovered that people who caught cowpox could not contract smallpox. In 1796, he inoculated a boy with exudates from cowpox lesions; the boy caught cowpox and subsequently did not contract smallpox. This principle of using a less harmful agent to confer protection against a more virulent one is a cornerstone of vaccination. Louise Pasteur (1822-1895) and his team created vaccinations for anthrax and rabies.

• Acquired Immunity: Immunization relies on the principles of acquired immunity.

  • Active Immunity: This involves the person’s own immune system responding to an antigen by producing antibodies and memory cells. This can be achieved:

    • Naturally: By suffering from a disease or a subclinical infection (e.g., measles providing lifelong immunity).

    • Artificially: Through vaccination, where killed or attenuated (weakened) pathogens, or parts of pathogens (antigens), are introduced into the body to stimulate an immune response without causing significant disease. This leads to the formation of memory cells, providing long-term protection. “Protecting patients with appropriate use of prophylactic anti-microbial, nutrition and vaccination” (page 36) and “Vaccination of health care workers” (page 40) are examples of applying this principle.

  • Passive Immunity: This involves an individual receiving pre-formed antibodies produced by someone else, providing immediate but short-lived protection as these antibodies are gradually broken down. This can occur:

    • Naturally: Maternal antibodies crossing the placenta to the fetus, or through breast milk.

    • Artificially: By administering ready-made antibodies, such as Anti-tetanus serum, Antivenom, or Antirabies, for prophylaxis (to prevent disease development after exposure) or therapeutic purposes (to prevent worsening of an existing disease).