ERIC KIM ₿

The physiology of how vaccines work

Vaccines work by stimulating the body’s immune system to recognize and fight specific pathogens, such as viruses or bacteria, without causing the actual disease. Below is a detailed explanation of the physiology behind how vaccines function:

1. Introduction of Antigens

  • Vaccines contain antigens, which are molecules that the immune system identifies as foreign. These antigens can be:
  • Weakened or inactivated forms of the pathogen.
  • Parts of the pathogen, like proteins.
  • Genetic material (e.g., mRNA) that instructs the body to produce the antigen.
  • Importantly, these antigens mimic the pathogen but are designed not to cause illness.

2. Immune System Activation

  • When a vaccine is administered (e.g., via injection or oral dose), the antigens are detected by the immune system.
  • Antigen-presenting cells (APCs), such as dendritic cells, capture the antigens and present them to T cells and B cells, key components of the adaptive immune system.
  • This triggers an immune response similar to what occurs during a real infection.

3. Production of Antibodies

  • B cells recognize the antigens and, with assistance from helper T cells, produce antibodies.
  • Antibodies are specialized proteins that:
  • Bind to the antigens.
  • Neutralize them or mark them for destruction by other immune cells.
  • Over time, the body produces different types of antibodies, with IgG being critical for long-term immunity.

4. Activation of T Cells

  • Helper T cells (CD4+ T cells):
  • Coordinate the immune response by assisting B cells in antibody production and activating other immune cells.
  • Cytotoxic T cells (CD8+ T cells):
  • Learn to identify and destroy cells infected by the pathogen.
  • This combination of antibody production and T cell activation creates a robust defense against the pathogen.

5. Formation of Memory Cells

  • A key feature of vaccination is the creation of memory B cells and memory T cells.
  • These cells “remember” the specific antigens introduced by the vaccine and remain in the body long after the initial immune response.
  • If the person is later exposed to the actual pathogen, memory cells trigger a rapid and powerful immune response, preventing the disease from developing.

6. Long-Term Protection

  • The presence of memory cells ensures that the immune system can respond quickly and effectively to future encounters with the pathogen.
  • This rapid response stops the infection before it can cause significant harm, providing long-term protection.

How Different Vaccine Types Work

While the core mechanism remains the same—introducing antigens to stimulate an immune response—different types of vaccines achieve this in unique ways:

  • Live attenuated vaccines (e.g., measles, mumps, rubella):
  • Use a weakened form of the pathogen that can replicate but doesn’t cause disease.
  • Often provide strong, long-lasting immunity with fewer doses.
  • Inactivated vaccines (e.g., polio, hepatitis A):
  • Use killed pathogens.
  • May require multiple doses for full immunity.
  • Subunit vaccines (e.g., HPV, hepatitis B):
  • Contain only specific parts of the pathogen, like proteins.
  • mRNA vaccines (e.g., COVID-19 vaccines):
  • Deliver genetic instructions for the body to produce the antigen itself.

Regardless of the type, all vaccines train the immune system to recognize and respond to the pathogen’s antigens.

Summary

In essence, vaccines work by introducing antigens that mimic a specific pathogen, prompting the immune system to produce antibodies and activate T cells. This process generates memory cells that provide long-term protection, enabling a swift and effective response if the pathogen is encountered later. Through this physiological mechanism, vaccines prevent infectious diseases without the individual having to experience the illness firsthand.

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