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Low Durability in Contemporary Vaccines

  • Context (TH): Contemporary Vaccines today often display low durability in maintaining protective immunity.
  • Recent research conducted a review of 34 licensed vaccines, revealing that only a minority provide prolonged protection exceeding 20 years.

Durability of Vaccines - PMF IAS

Vaccination

  • Vaccines play a crucial role in bolstering our immune system’s defenses against harmful pathogens.
  • They aim to mimic natural infections without causing illness.
  • Primary immune response: After vaccination, B cells produce antibodies.
  • Secondary immune response: Upon re-exposure (boosters or actual pathogen encounter), memory B cells and LLPCs kick into action.

How do the vaccines work?

Working of Vaccines - PMF IAS

  • Introduction of Antigens:
    • Vaccines contain either weakened or inactivated forms of the pathogen (such as viruses or bacteria) or specific parts of the pathogen (like proteins).
    • When we receive a vaccine, these antigens are introduced into our body.
  • Immune System Activation:
    • Our immune system recognizes these antigens as foreign invaders.
    • Specialized cells, such as B cells and T cells, respond to the antigens.
  • B Cell Response:
    • B cells produce antibodiesproteins that specifically target the pathogen.
    • These antibodies bind to the antigens, neutralizing them and preventing infection.
  • Memory Cells Formation:
    • Some B cells become memory B cells.
    • These memory cells “remember” the pathogen and remain in our system for a long time.
  • T Cell Response:
    • T cells play a critical role in coordinating the immune response.
    • They help B cells produce antibodies and directly attack infected cells.

Long-term Immune Protection

  • Memory B Cells and Long-Lived Plasma Cells (LLPCs): Memory B cells and LLPCs are key players in long-term immune protection.
    • They form after exposure to a pathogen (or a vaccine) and persist in our body for extended periods.
  • Memory B Cells:
    • Function: Memory B cells “remember” specific pathogens.
    • Location: They reside in secondary lymphoid tissues (such as lymph nodes and spleen) and circulate in the blood.
    • Response: When the same pathogen reappears, memory B cells quickly differentiate into plasma cells, producing specific antibodies.
    • Durability: Memory B cells can persist for years or even decades.
  • LLPCs:
    • Function: LLPCs are antibody factories.
    • Location: They primarily reside in the bone marrow.
    • Response: When needed, LLPCs churn out antibodies against the pathogen.
    • Durability: LLPCs can survive for a very long time—sometimes a lifetime.
  • Some vaccines contain trace amounts of substances like aluminium (used to enhance immune response) and mercury (in the form of thimerosal, used as a preservative).

Factors that contribute to the disparity in Vaccine Durability

Vaccine Type

  • Live attenuated vaccines (e.g., measles, mumps, rubella):
    • Mimic natural infection closely.
    • Generate robust memory B cells and long-lived plasma cells (LLPCs).
    • Provide long-lasting immunity.
  • Inactivated vaccines (e.g., flu shots):
    • May not induce LLPCs as effectively.
    • Require periodic boosters.

Antigen Persistence

  • Some vaccines maintain antigen presence longer (e.g., live vaccines).
  • Prolonged antigen exposure enhances memory cell formation.

Adjuvants

  • Adjuvants (like aluminium salts) enhance immune responses.
  • They influence memory cell development.

Route of Administration

  • Different routes (intramuscular, oral, nasal) impact immune memory.
  • Intramuscular vaccines often generate robust responses.
  • Pathogen Variation:
    • Some pathogens mutate rapidly (e.g., influenza virus).
    • Antigenic changes require frequent vaccine updates.
  • Antigen Complexity:
    • Complex pathogens (e.g., HIV) challenge vaccine design.
    • Generating effective immune memory is difficult.
  • Persistence of Pathogen:
    • Some pathogens (e.g., hepatitis B virus) persist in the body.
    • Vaccines must maintain immune memory over time.
  • Individual Variation:
    • Genetics, age, health status influence responses.
    • Some individuals mount stronger reactions than others.
  • Immunosuppression:
    • Immunosuppressed individuals (e.g., transplant recipients) may have weaker immune memory.
    • Vaccination strategies must consider such populations.

Way Forward

  • Develop vaccines that stimulate robust and durable responses.
  • Tailor vaccines based on individual factors.
  • Design effective booster schedules.
  • Boost memory cell responses when needed.
  • Address disparities in vaccine access and equity.
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