Context:
A recent review of several vaccines revealed that only five offer protection lasting more than 20 years, and merely three provide lifelong immunity. This variability in vaccine efficacy raises concerns about the durability and effectiveness of immunization strategies. The findings underscore the need for ongoing research and development to enhance vaccine longevity and effectiveness, addressing challenges associated with waning immunity and ensuring sustained protection against infectious diseases.
Relevance:
GS II: Health
Dimensions of the Article:
- Vaccines and Immunological Mechanism Explained
- Vaccine and its Efficacy
- Factors Influencing Vaccine Efficacy
Vaccines and Immunological Mechanism Explained
What are Vaccines?
- Definition: Vaccines are biological formulations designed to activate the immune system against specific pathogens like viruses or bacteria, without causing illness.
- Composition: They often contain weakened or inactivated pathogens, pathogen parts, or toxins produced by the pathogen.
Immunological Mechanism of Vaccines:
Memory B Cells:
- Formation: Generated in lymph nodes post-vaccination, these cells “remember” antigens, facilitating swift antibody production upon future antigen exposure.
T Cell Support:
- Role: Memory B cells rely on T cell assistance; vaccines stimulating T cells can initiate memory B cell production.
Variability in B Cell Response:
- Not all vaccines induce memory B cell production; some require regular boosters to prolong immunity.
- Example: Measles and rubella vaccines sustain consistent memory B cell levels and antibody levels for decades, contrasting with chickenpox, tetanus, and diphtheria vaccines.
Long-Lasting Plasma Cells (LLPCs):
- Migration: These cells move to the bone marrow and can persist for extended periods, contributing to vaccine-induced immunity.
- Importance: LLPCs are crucial for enduring protection, representing an immunological “holy grail.” Vaccine development aims to generate LLPCs for sustained immunity.
- Example: mRNA Covid-19 vaccines may not activate LLPCs in the bone marrow, potentially affecting long-term immunity.
Variability in Vaccine Efficacy:
- Different vaccines have varying abilities to stimulate memory B cells and LLPCs, leading to differences in duration and effectiveness of immunity.
Vaccine and its Efficacy:
| Measles Vaccine Type: Live attenuated virus Efficacy: One dose: Around 93% effective, Two doses: Around 97% effective Schedule: Typically administered in two doses, first dose at 12-15 months and the second dose at 4-6 years Duration: Lifelong protection for most individuals after two doses |
| Rubella Vaccine Type: Live attenuated virus (often combined with measles and mumps vaccine, known as MMR) Efficacy: One dose: Around 95% effective Two doses: Over 99% effective Schedule: Two doses, first at 12-15 months and the second at 4-6 years (usually given as MMR) Duration: Lifelong protection for most individuals after two doses. |
| Yellow Fever Vaccine Type: Live attenuated virus Efficacy: Around 99% effective Duration: Provides lifelong protection for most people Schedule: Single dose, often required for travel to endemic regions |
| Hepatitis B Vaccine Type: Recombinant vaccine (contains viral surface antigen) Efficacy: Three doses: Over 95% effective in preventing infection Schedule: Three doses, typically given at 0, 1-2 months, and 6 months Duration: Long-term protection, possibly lifelong for many individuals after completing the three-dose series |
| Inactivated Hepatitis A Vaccine Type: Inactivated virus Efficacy: Two doses: Over 95% effective Schedule: Two doses, first dose followed by a booster 6-12 months later Duration: Protection for at least 20 years after completing the two-dose series, and possibly longer |
Factors Influencing Vaccine Efficacy
Vaccine efficacy is determined by various factors categorized into vaccine-related, pathogen-related, and host-related factors.
Vaccine-Related Factors:
- Type of Vaccine:
- Live Viral Vaccines: Vaccines like measles, rubella, yellow fever, chickenpox, and oral polio typically offer longer-lasting protection compared to killed or subunit vaccines.
- Interval Between Doses:
- Timing: A longer interval, ideally at least six months, between priming and booster doses is essential for eliciting a robust immune response.
Pathogen-Related Factors:
- Nature of Infection:
- Mucosal Infections: Pathogens causing mucosal infections, such as SARS-CoV-2 and influenza, can lead to frequent reinfections due to rapid transmission before the immune system responds adequately.
- Genetic Stability:
- Mutation Rates: RNA viruses like measles and SARS-CoV-2, which mutate frequently, may necessitate vaccine updates to maintain efficacy.
- Vaccine Adaptation: While the measles vaccine remains stable, updates to SARS-CoV-2 vaccines have been required due to mutations.
Host-Related Factors:
- Demographics:
- Age, Gender, and Obesity: Factors like extreme ages, gender differences, and obesity can influence vaccine efficacy and the duration of protective immunity.
-Source: The Hindu
