Explain that vaccines contain antigens that stimulate immune responses to provide long‑term immunity.
Key Concepts
Antigen: Any substance that can be recognised by the immune system, typically a protein or polysaccharide on the surface of a pathogen.
Antibody (Immunoglobulin): A Y‑shaped protein produced by B‑cells that binds specifically to an antigen, neutralising it or marking it for destruction.
Vaccination: The deliberate introduction of a harmless form of an antigen to provoke an immune response without causing disease.
Immunological memory: Long‑term protection generated by memory B‑cells and T‑cells after the first exposure to an antigen.
How \cdot accines Work
The vaccine delivers an antigenic component (e.g., inactivated pathogen, protein subunit, or genetic material).
Antigen‑presenting cells (APCs) ingest the antigen and display fragments on MHC molecules.
Helper T‑cells recognise the antigen–MHC complex and activate B‑cells.
Activated B‑cells differentiate into plasma cells that secrete specific antibodies.
Some B‑cells become memory cells, persisting for years and enabling a rapid response on re‑exposure.
Types of \cdot accines and Their Antigenic Forms
Vaccine Type
Antigenic Component
Typical Immune Response
Live‑attenuated
Weakened whole organism
Strong cellular and humoral immunity; often lifelong protection
Inactivated (killed)
Whole organism rendered non‑viable
Primarily humoral response; booster doses usually required
Subunit / Recombinant
Purified protein or polysaccharide antigen
Targeted antibody response; safe for immunocompromised individuals
mRNA
mRNA encoding a specific viral protein (e.g., spike protein)
Both antibody and cellular responses; rapid development cycle
Viral vector
Non‑replicating virus carrying gene for antigenic protein
Robust cellular and humoral immunity
Long‑Term Immunity: The Role of Memory Cells
After vaccination, two main populations of memory cells are generated:
Memory B‑cells: Remain in circulation and quickly differentiate into plasma cells upon re‑exposure, producing large quantities of high‑affinity antibodies.
Memory T‑cells: Include both helper (CD4⁺) and cytotoxic (CD8⁺) subsets that accelerate the cellular immune response.
The presence of these cells means that a subsequent encounter with the actual pathogen triggers a rapid, amplified response, often neutralising the pathogen before disease develops.
Key Points to Remember
Vaccines are antigenic preparations that mimic natural infection without causing disease.
The immune system’s primary response to a vaccine generates antibodies and memory cells.
Booster doses reinforce memory, extending the duration of protection.
Different vaccine platforms present antigens in distinct ways, influencing the type and strength of immunity.
Suggested diagram: Flowchart showing the steps from vaccine administration to memory B‑cell formation and long‑term immunity.