Vaccination Types and Their Mechanisms

Different Vaccine Types

• Various vectors can be used to initiate immunity, including:
  • Synthetic peptides (pieces of proteins)
  • Whole inactivated viruses
  • Live attenuated viruses (mutated to be non-infectious)
  • DNA vaccines

Live Attenuated Vaccines

• Definition: Contain live pathogens that are modified to be non-infectious.
• Pros:
  • Produces the most robust immune response similar to natural infection.
  • Usually does not require booster shots.
• Cons:
  • Small chance of reversion to pathogenic form.
  • Can have serious side effects.
  • Requires cold chain storage, making it more expensive to transport.

Inactivated Vaccines

• Types: Can be classified into whole agent and subunit vaccines.
  • Whole Agent: Entire pathogen is administered, killed by heat or chemicals.
  • Subunit: Uses only a part of the microbe, typically antigenic fragments.
• Pros:
  • Safer; no risk of reversion to pathogenic state.
  • Stimulates B cell response.
• Common Examples: Flu (A strain), polio, rabies (can be given post-exposure).
• Cons:
  • Weaker immune response; requires booster shots (e.g., flu annually).
  • Possible denaturation of proteins during inactivation can affect efficacy.

Toxoid Vaccines

• Definition: Vaccines made from toxins produced by pathogens, modified to be non-toxic (toxoids).
• Common Uses: Vaccinations against diseases such as tetanus and diphtheria.
• Pros:
  • Similar to subunit vaccines, promotes immune response without introducing toxicity.
• Cons:
  • Immune response may not be as strong; booster shots needed every 10 years.

mRNA Vaccines

• Mechanism: Utilizes the central dogma (DNA → RNA → Protein) to induce immunity.
  • Isolates mRNA that codes for viral proteins (e.g., the spike protein in SARS-CoV-2).
• Pros:
  • Activates both B and T cell response, promoting strong long-term immunity.
  • Specific and easier to manufacture; poses no risk of reverting to pathogenic form.
• Delivery: Lipid nanoparticles facilitate entry into host cells, allowing for translation of proteins.
• Common Examples: Pfizer and Moderna COVID-19 vaccines.
• Cons:
  • mRNA is unstable; requires low-temperature storage, complicating distribution and production.
  • Potential for mild side effects indicating a robust immune response (e.g., fever, fatigue).