Exploring the Durability of Modern Vaccines | 10 Apr 2024

Source: TH

Why in News?

Recently, in a review of several vaccines, it has been found that only five vaccines provide long-lasting protection spanning more than 20 years and only three provide lifelong protection.

• The variability in vaccine efficacy poses challenges concerning its effectiveness and longevity.

What are Vaccines and Immunological Mechanism?

• About:
  • Vaccines are biological preparations designed to stimulate the body's immune system to recognise and fight against specific pathogens, such as viruses or bacteria, without causing the disease itself.
  • They typically contain weakened or inactivated forms of the pathogen, parts of the pathogen, or toxins produced by the pathogen.
• Immunological Mechanism :
  • Memory B Cells: Formed in lymph nodes after vaccination, they "memorise" antigens and trigger rapid antibody production upon subsequent exposure to the same antigen.
  • T Cell Support: Memory B cells require T cell support vaccines that stimulate T cells can induce the production of memory B cells.
  • Variability in Vaccine-Induced B Cell Response: Not all vaccines prompt the body to produce memory B cells. Some vaccines require frequent boosters to enhance immunity duration.
    • Example: Measles and rubella vaccines maintain constant levels of memory B cells in blood plasma, correlating with antibody levels for decades. However, this is not observed with chickenpox, tetanus, and diphtheria vaccines.
  • Long-Lasting Plasma Cells (LLPCs): Migrate to the bone marrow and may endure for decades, playing a crucial role in vaccine-induced immunity.
    • LLPCs are essential for lifelong protection, termed the immunology "holy grail." Vaccines aim to generate LLPCs for sustained immunity.
    • Some vaccines, like mRNA Covid-19 shots, fail to activate LLPCs in the bone marrow, potentially impacting long-term protection.
  • Variability in Vaccine Efficacy: Different vaccines differ in their ability to produce memory B cells and LLPCs, leading to discrepancies in durability and effectiveness.
• Vaccine and its Efficacy:

What Factors Influence the Efficacy of Vaccines?

• Vaccine efficacy is influenced by three primary categories of factors, i.e., vaccine related, pathogen related and host related.
  • Vaccine Related:
    • Live Viral Vaccinations: It Includes the vaccines for measles, rubella, yellow fever, chickenpox, and polio (oral) provide long lasting protection than killed pathogen or subunit vaccines.
    • Interval Between Vaccine Doses: A long interval of at least six months between priming and booster doses is crucial for a robust immune response.
  • Target Pathogen Related:
    • Pathogens with Mucosal Infections: Viruses causing mucosal infections like SARS-CoV-2 and influenza lead to frequent reinfections due to their quick transmission before the immune system can mount a response.
    • Genetic Stability of Virus: RNA viruses like measles and SARS-CoV-2, with high mutation rates, may require vaccine updates.
      • Measles vaccine has remained stable, while SARS-CoV-2 vaccines have been updated due to mutations.
  • Host-Related Factors:
    • Age, Gender, and Obesity: These factors influence vaccine efficacy and duration of immunity. Extreme ages and obesity may lead to shorter-lasting immune responses.