Study Notes on Vaccines, Immunity, and Vaccine Hesitancy

Lecture Overview

  • Topic: Vaccines and Vaccine Preventable Diseases

  • Key Points Covered:

    • Categories of Adaptive Immunity

    • Vaccine Formulations

    • Childhood vaccines

    • Social dynamics of Vaccines and Anti-vaccine sentiments

  • Source Material:

    • Openstax Microbiology textbook

    • Chapter 18: Adaptive Immune Responses

Categories of Adaptive Immunity

Types of Immunity

  • Active Immunity

    • Natural:

    • Immune response to natural infection.

    • Generates specific memory cells.

    • Artificial:

    • Immune response induced by vaccination.

    • Generates specific memory cells.

  • Passive Immunity

    • Natural:

    • Antibodies passed from mother to child.

    • Provides short-term immunity only.

    • Artificial:

    • Immune therapy using a serum containing antibodies.

    • Provides short-term immunity only.

Four Classifications of Immunity

  • Visual reference to the classifications presented in the course materials.

Vaccines and Immune Response

How Vaccines Work

  • Vaccination promotes Artificial Active Immunity.

  • Mechanism:

    • Exposure to the antigens in the vaccine triggers an immune response.

    • Leads to the formation of memory cells and antibodies targeting the specific antigens.

  • Upon later exposure to the actual pathogen, these memory cells respond promptly to prevent infection.

  • Long-term protection: Vaccines do not offer immediate immunity; about ~2 weeks are needed for antibody levels to reach protective levels.

History of Vaccination

Early Practices

  • Variolation:

    • Originated in the Far East as a method for smallpox prevention, later spread to Europe and Africa.

Key Historical Figures

  • Edward Jenner (1796):

    • Discovered immunity from smallpox through exposure to cowpox.

    • Utilized scrapings from cowpox lesions, recognized as an early form of vaccination.

    • Term “vaccination” arises from the Latin word “vacca” meaning cow.

  • Louis Pasteur (1850s):

    • Developed early vaccines for rabies and anthrax, paving the way for modern immunology.

    • Approximately 25 diseases are preventable by vaccines today.

    • Achievements include the eradication of smallpox in 1980 with the current aim of eradicating polio.

Vaccine Formulations

Types and Categories of Vaccines

  • Vaccination Definition: Injection of one or more microbial antigens for protection against future disease.

  • **Active Agent Vaccines:

    • Live attenuated Vaccines**:

    • Contain live microbes that multiply in the host but are weakened to not cause disease.

    • Examples: Varicella-zoster, MMR, Rotavirus.

    • Recombinant Vector Vaccines:

    • Genetic information from the pathogen is delivered via a harmless carrier virus.

    • Examples: Ebola, Johnson & Johnson COVID-19 vaccines.

    • Inactivated Agent Vaccines:

    • Include whole-cell or inactivated viruses.

    • Examples: Polio (IPV), Hepatitis A, certain influenza vaccines.

    • Subunit Vaccines:

    • Comprise parts of the pathogen (immunogenic components).

    • Require adjuvants to boost immune response.

    • Toxoid Vaccines:

    • Inactivated toxins from pathogens.

    • Examples: Diphtheria, Tetanus.

    • DNA/RNA Vaccines:

    • Contain genetic material to produce antigens within host cells.

    • Modern examples include certain COVID-19 vaccines (Pfizer, Moderna).

Properties and Safety of Vaccines

Safety and Immune Capacity

  • Vaccine administration involves a very small fraction of the immune system's theoretical capacity:

    • Childhood Vaccination: Current standards = 0.1% of immune capacity with 11 vaccines administered at once.

    • Historically, vaccination in the 1960s involved ~3000 antigens, with a decrease to 150 antigens in 2019.

Herd Immunity

  • Concept: Communal immunity protects those who are unvaccinated when the majority of the population is vaccinated, reducing disease spread.

  • Focus on creating herd immunity through immunization programs encourages broader vaccination compliance.

Vaccine Hesitancy

Understanding Vaccine Hesitancy

  • Definition: Delay in vaccine acceptance or refusal despite availability.

  • Influenced by:

    • Complacency, convenience, and confidence in vaccines

    • Perceptions, safety concerns, social norms, and availability.

Reasons for Hesitancy

  • Common causes of hesitancy include:

    • Misconceptions regarding safety (e.g., autism claims later retracted).

    • Distrust of scientific processes and claims regarding natural infections.

    • Cultural or religious objections, especially regarding fetal tissue origins of some vaccines.

Ethical Considerations

Vaccine Development Concerns

  • Production of vaccines sometimes involves chicken eggs, animal cells, or human tissues, raising ethical questions particularly about the use of cells derived from fetal tissues.

Current Use of Fetal Cell Lines

  • Two significant cell strains used: WI-38 (1962, U.S.) and MRC-5 (1970, U.K.) continue to be used in producing vaccines.

  • Examples of vaccines developed using these cell lines:

    • Hepatitis A, Rubella, Varicella, Zoster, Adenovirus, Rabies vaccines.

  • Estimated impact of these vaccines includes:

    • Nearly 11 million deaths prevented and 4.5 billion disease cases averted.

Learning Objectives

After the lecture and readings, students should be able to:

  • Name and describe the four categories of adaptive immunity.

  • Identify fundamental immunological principles of vaccination.

  • Compare and contrast various types of vaccine formulations.

  • Define adjuvants and describe their purpose.

  • Discuss vaccine hesitancy and the factors contributing to re-emergence of vaccine-preventable diseases.

  • Explain herd immunity and how it safeguards non-immunized individuals.

  • Identify key information regarding the smallpox virus: mode of transmission, incubation period, innate immune defenses affected, and overall mortality rate.