Vaccines work by training the body's immune system to recognize and fight specific disease-causing organisms without causing the actual disease. They do this by introducing an antigen, which is a substance that mimics parts of a virus or bacteria, into the body. This antigen can be a weakened or inactivated form of the pathogen, a piece of it, or genetic instructions for the body to produce the antigen itself. When the vaccine's antigen enters the body, immune cells called antigen-presenting cells (APCs) detect and consume it, then display parts of the antigen to other immune cells like T-cells and B-cells. This triggers the immune system to produce antibodies and activate cells that remember the pathogen. If the vaccinated person later encounters the real pathogen, their immune system can respond quickly and effectively to prevent illness or reduce its severity
. Different types of vaccines include:
- Live attenuated vaccines: Contain weakened forms of the pathogen.
- Inactivated vaccines: Contain killed pathogens.
- Subunit, recombinant, or protein-based vaccines: Contain pieces of the pathogen, such as proteins.
- mRNA vaccines: Provide genetic instructions for cells to produce a harmless piece of the pathogen (like the spike protein in COVID-19), triggering an immune response without using the live virus.
- Viral vector vaccines: Use a harmless virus to deliver genetic material that instructs cells to make a pathogen protein to stimulate immunity
Vaccination not only protects the individual but also contributes to herd immunity, reducing the spread of disease in the community and protecting those who cannot be vaccinated due to health reasons
. In summary, vaccines safely expose the immune system to a part or a mimic of a pathogen, enabling the body to develop antibodies and memory cells that provide long-lasting protection against future infections
