Vaccination

Understanding How Vaccines Work

  • Immune Response Mechanism:
      - Vaccines enhance memory immune response. This means that vaccines help the immune system remember how to fight off specific pathogens more effectively in the future.   - Upon first exposure to a pathogen, the immune response is slow. The body needs time to recognize the invader and begin fighting it, which often involves the creation of new immune cells.   - Subsequent exposures lead to quick immune reactions due to memory T and B cells. These cells remember the pathogen and allow the immune system to respond much faster, usually without the person even getting sick.

  • Antigen Presenting Cells (APCs):
      - Include macrophages, which consume pathogens and present their antigens on cell surfaces. Macrophages are a type of white blood cell that play a crucial role in identifying and destroying pathogens.   - Antigens are portions of proteins or cell walls recognized by the immune system. They are the specific parts of the pathogen that trigger an immune response.

  • T Cells and Immune Activation:
      - T cells recognize antigens from APCs and proliferate. This means that once T cells have seen an antigen, they multiply to increase the body’s defense against that pathogen.   - Formation of T helper cells which further stimulate immune responses. These helper cells are important because they signal other immune cells to take action.   - B cells develop into effector B cells, memory B cells, or plasma cells to produce antibodies. Antibodies are proteins that specifically target and neutralize pathogens.

  • Memory Cells:
      - Key focus on memory B cells and memory T cells which provide long-term immunity. These cells persist long after the initial infection has been cleared, ready to respond quickly if the pathogen is encountered again.   - Upon re-exposure to the antigen, a rapid immune response occurs without symptomatic infection (inapparent reinfection). This rapid response usually prevents reinfection from causing illness.

  • Phases of Immune Response:
      - Initial response takes time (innate immune system). The first phase involves various defenses that respond immediately or within hours of an antigen's appearance in the body; this is not specific to a particular pathogen.   - Immune response peaks and then declines (protective immunity). During this phase, the body is actively fighting the infection, and then gradually the immune response decreases once the pathogen is eliminated.   - Memory phase allows the body to respond swiftly to later infections. In this phase, the immune system is ready to attack any future invasions by the same pathogens quickly.

Types of Vaccines

  • Three primary types of vaccines:
      1. Live Attenuated Vaccines:
         - Weakened pathogens that can cause mild infections without severe symptoms. These vaccines expose the immune system to a version of the pathogen that cannot cause disease but still stimulates an immune response.   

  • 2. Inactivated Vaccines:
         - Pathogens that are killed or destroyed, no longer able to replicate. These vaccines cannot cause disease and need multiple doses to build immunity.   

  • 3. Subunit/Vaccines:
         - Made from specific components such as proteins or polysaccharides, including toxoid vaccines (modified toxins). These vaccines contain parts of the pathogen rather than the whole germ, making them very safe.

Childhood Vaccinations

  • Hepatitis B Vaccine:

    •   -First vaccine administered at birth to protect against Hepatitis B, which can be transmitted from mother to child. Hepatitis B is a serious liver infection that can be transmitted during childbirth or through contact with infected blood.   

    • Typically administered as a protein vaccine in three doses within the first eighteen months. Each dose is crucial for building up immunity over time.

  • Hepatitis A Vaccine:
      - Inactivated virus vaccine given in two doses; first dose around one year old. Hepatitis A is transmitted through contaminated food and water, making vaccination important for children.

  • Rotavirus Vaccine:
      - Common cause of diarrhea in infants, preventive vaccines are Rotatec (2 doses) and RotaTeq (3 doses, less potent). Rotavirus can cause severe dehydration, which is dangerous for young children.

  • DTaP Vaccine (Diphtheria, Tetanus, Acellular Pertussis):
      - Composed of multiple bacterial vaccines, requires four doses in the first seven years of life. This vaccine helps protect against three serious diseases.   

  • - Differentiation between DTaP (for children) and Tdap (booster for adolescents/adults). The booster helps to maintain immunity going into adulthood.

  • Haemophilus influenzae Type B Vaccine:
      - A polysaccharide vaccine received in 3 to 4 doses within the first fifteen months. This vaccine protects against a bacteria that can cause severe infections, especially in children.

  • Streptococcus pneumoniae Vaccine:
      - Pneumococcal Polysaccharide vaccine with four doses given in the first fifteen months. This vaccine helps protect against pneumonia and meningitis.

  • Polio Vaccine:
      - Critical in reducing infections globally from 350,000 in 1988 to 33 in 2018. Polio is a debilitating disease that can lead to paralysis.  

  • - Two forms: Live attenuated and inactivated; used based on infection risk geography. The live vaccine can provide better community immunity, while the inactivated version is safer but effective in lower-risk areas.   

  • - Live vaccine can revert and cause mild infections; inactivated version is safer but less effective in low-risk areas.

  • MMR Vaccine (Measles, Mumps, Rubella):
      - Administered to prevent severe congenital defects from rubella in newborn females. This vaccine is crucial for preventing these diseases, which can lead to serious health complications.   

  • - Controversially re-emerged due to anti-vaccination sentiments, now given in two doses within the first six years. Public concern and misinformation have made vaccination levels drop in some communities, increasing risks for outbreaks.

  • Flu Vaccine:

    • Annual updates required due to antigenic drift of H and N proteins (e.g., H1N1, H3N2). Every year, the flu vaccine is updated because the virus changes, necessitating a new vaccine to match circulating strains.

    • Composition may be trivalent or quadrivalent for protection against multiple strains. Trivalent targets three strains, while quadrivalent covers four.  

    • Can be administered via intramuscular injection (inactivated) or nasal mist (live attenuated). Different methods allow for options based on patient preferences.

  • Other Vaccines:
      - HPV, meningitis, yellow fever, typhoid, rabies, and shingles vaccines discussed briefly. Each of these vaccines targets specific diseases that can be very serious.   - Shingles vaccine provided to prevent reactivation of varicella zoster virus in older adults. Shingles can be extremely painful and disabling, hence the need for vaccination in older populations.

Vaccine Controversies

  • Vaccine Concerns and Autism Link:
      - Misinterpretation of correlation vs. causation; speculations linking vaccines to autism arose from faulty studies. It’s essential to differentiate between mere associations and actual cause-and-effect relationships.   - Misleading claims led to decreased vaccination rates and increased disease outbreaks. This created a public health crisis as fewer people are immunized against preventable diseases.

  • Scientific Community Response:
      - Discrediting of Andrew Wakefield's paper claiming link between vaccines and autism. The medical community has stood firm in debunking these false claims with extensive research.   - Acknowledgment of the retraction and licensing revocation of Wakefield by medical organizations. This demonstrates the commitment of the scientific community to uphold evidence-based medicine.

  • Adjuvants and Preservatives:

    • Concerns regarding aluminum compounds not substantiated; present in breast milk at higher levels than in vaccines. This shows that vaccines, which contain minimal amounts of these compounds, are generally safe

    • Thimerosal (ethylmercury, not methylmercury) previously included but removed to address parental fears without evidence of harm. The removal increased public confidence in vaccine safety.

    • Formaldehyde's prevalence in normal metabolism compared to vaccine quantities reaffirmed as not significant concerns. This points to how vaccines are rigorously tested for safety before being approved.

Conclusion

  • Importance of solid scientific information for informed vaccine decision-making. Keeping the public informed based on accurate scientific data is vital in retaining trust in vaccines.

  • Emphasis on educating parents rather than condemning their fears, stressing the necessity for herd immunity to protect vulnerable populations. Public health initiatives must strive to clear up misconceptions and provide supportive information to encourage immunization for the safety of all.