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This is the complete lecture note for COM409 Immunity and Immunisation Programme. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: COM 409 Course title: Immunity and Immunisation Programme Course credit load: 1 Unit Series 1: Concepts of Immunity and Immunisation • Part 1.1: Definitions and Types of Immunity o Sub Part 1.1.1: Definition of immunity o Sub Part 1.1.2: Innate and adaptive immunity o Sub Part 1.1.3: Active and passive immunity • Part 1.2: Immunisation and Vaccination o Sub Part 1.2.1: Definition and distinction between immunisation and vaccination o Sub Part 1.2.2: Types of vaccines o Sub Part 1.2.3: Mechanisms of vaccine-induced protection • Part 1.3: Herd Immunity and Its Public Health Significance o Sub Part 1.3.1: Definition and concept of herd immunity o Sub Part 1.3.2: Herd immunity thresholds for key diseases o Sub Part 1.3.3: Challenges to achieving herd immunity in Nigeria
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Introduction Immunity is the foundation upon which immunisation programmes are built. Before one can appreciate why vaccines work, how they should be delivered, or why some communities remain vulnerable to outbreaks despite vaccination programmes, one must first understand what immunity is and how the body acquires and maintains it. These biological concepts translate directly into public health practice, determining how immunisation schedules are designed and why herd immunity is a programme goal, not merely an outcome. The aim of this Series is to define immunity and its types, distinguish immunisation from vaccination, describe the major types of vaccines and their mechanisms, and explain the concept of herd immunity and its significance for Nigeria public health practice. We shall commence by defining immunity and examining innate, adaptive, active, and passive forms. Next, we will examine immunisation and vaccination, including vaccine types and mechanisms. Finally, we will close by examining herd immunity, its thresholds for key diseases, and the challenges of achieving it in Nigeria. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 define immunity and distinguish between its major types, • SLO 1.2 distinguish between immunisation and vaccination, • SLO 1.3 describe the major types of vaccines and explain how they induce protective immunity, • SLO 1.4 define herd immunity and state the threshold required for key vaccine-preventable diseases, and • SLO 1.5 identify the challenges to achieving herd immunity in Nigeria.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.1 Definitions and Types of Immunity 1.1.1 Definition of immunity Immunity is the ability of an organism to resist a specific infectious disease by deploying biological mechanisms that prevent pathogens from invading, proliferating, or causing harm. In humans, this capacity is provided by the immune system, a complex network of cells, tissues, and molecular signals distributed throughout the body. Immunity may be complete (providing full protection against infection) or partial (reducing the severity or duration of illness without preventing infection entirely). From a public health perspective, immunity is significant not only at the individual level but at the population level: when a sufficient proportion of a community is immune, the transmission chain of an infectious agent is interrupted, protecting even non-immune individuals. This population-level protection, known as herd immunity, is the primary goal of national immunisation programmes and determines the vaccination coverage targets that programmes must achieve to prevent outbreaks. Fill in the blank: Immunity is the ability of an organism to __________ a specific infectious disease by deploying biological mechanisms that prevent pathogens from invading, proliferating, or causing harm. 1.1.2 Innate and adaptive immunity Innate immunity is the first line of defence against pathogens, present from birth and responding rapidly but non-specifically to any foreign substance. It includes physical barriers (skin and mucous membranes), chemical barriers (stomach acid, antimicrobial proteins), cellular components (neutrophils, macrophages, natural killer cells), and the inflammatory response. Innate immunity does not improve with repeated exposure and does not produce immunological memory, but it is essential for immediate containment of infection while adaptive responses develop.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Adaptive (acquired) immunity is the second line of defence, developing over days following initial pathogen exposure. It involves B lymphocytes (which produce pathogen-specific antibodies) and T lymphocytes (which kill infected cells and regulate immune responses). Its defining feature is immunological memory: after first exposure, the immune system retains antigen-specific memory cells that enable a faster, stronger response upon re-exposure. This memory is the biological basis of both natural immunity from prior infection and vaccine-induced immunity. Fill in the blank: __________ immunity involves B and T lymphocytes, develops over days after pathogen exposure, and produces immunological memory enabling a faster, stronger response upon re-exposure. 1.1.3 Active and passive immunity Active immunity is acquired when a person own immune system mounts a response against a pathogen or its antigens, producing antibodies and memory cells. It can be acquired naturally, through infection with a pathogen (natural active immunity), or artificially, through vaccination with an antigen preparation that stimulates the immune system without causing disease (artificial active immunity). Active immunity is generally long-lasting because it involves immune memory, though the duration varies by disease and vaccine type. Passive immunity is acquired when pre-formed antibodies from another individual or source are transferred to a recipient, conferring immediate but temporary protection. Natural passive immunity occurs when maternal IgG antibodies cross the placenta to protect the foetus, and when secretory IgA is transferred through breast milk. Artificial passive immunity is provided through administration of immune globulin or antitoxin (for example, tetanus immunoglobulin after a contaminated wound). Passive immunity lasts only weeks to months, as transferred antibodies are gradually catabolised. Fill in the blank: __________ passive immunity occurs when maternal IgG antibodies cross the placenta to protect the foetus, providing the newborn with temporary protection against diseases the mother is immune to.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Figure 1.1: Types of immunity and their characteristics Pilot questions 1.1 1. Define immunity. 2. Distinguish between innate and adaptive immunity. 3. What is immunological memory and why is it significant? 4. Distinguish between active and passive immunity. 5. Give one example each of natural active immunity and natural passive immunity. 1.2 Immunisation and Vaccination 1.2.1 Definition and distinction between immunisation and vaccination Vaccination is the administration of a vaccine, a biological preparation containing antigens derived from a pathogen, into a person body to stimulate an immune response. Immunisation is
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS the process by which a person becomes immune to a disease, either through vaccination or through natural infection. The two terms are often used interchangeably but are technically distinct: vaccination is the act of administering the vaccine; immunisation is the outcome, the development of protective immunity following that act. Not every vaccination results in immunisation. A person may be vaccinated but fail to mount an adequate immune response due to factors such as immunosuppression, cold chain failures that have compromised vaccine potency, improper administration technique, or pre-existing immunity that masks the response. Conversely, immunisation can occur without vaccination, through natural infection. In public health reporting, vaccination coverage (the proportion vaccinated) and immunisation coverage (the proportion protected) may therefore differ, though vaccination coverage is more routinely measured. Fill in the blank: __________ is the act of administering a vaccine, while immunisation is the outcome, the development of protective immunity that may follow that act. 1.2.2 Types of vaccines Vaccines are classified by their composition and method of antigen presentation. Live attenuated vaccines contain a weakened form of the live pathogen that can replicate but does not cause disease in immunocompetent individuals, producing a strong, long-lasting immune response closely resembling natural infection (examples: measles, mumps, rubella, oral polio vaccine, BCG, yellow fever). Inactivated vaccines contain killed pathogen or purified components, are generally safer for immunocompromised individuals, but typically require multiple doses and booster shots (examples: injectable polio vaccine, hepatitis A, seasonal influenza). Subunit, recombinant, and conjugate vaccines contain only specific antigens or antigen fragments, reducing the risk of side effects while still inducing specific immunity (examples: hepatitis B, HPV, meningococcal conjugate, pneumococcal conjugate). Toxoid vaccines contain inactivated bacterial toxins, inducing immunity against the toxin rather than the organism itself (examples: tetanus and diphtheria toxoids). mRNA vaccines, introduced prominently during the COVID-19 pandemic, deliver genetic instructions for antigen production, representing a new class with rapid production potential and no risk of live pathogen exposure.
la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: Live __________ vaccines contain a weakened form of the live pathogen that can replicate but does not cause disease, producing a strong, long-lasting immune response resembling natural infection. 1.2.3 Mechanisms of vaccine-induced protection Vaccines protect through three primary mechanisms. First, by stimulating the production of pathogen-specific antibodies (humoral immunity) that neutralise the pathogen or mark it for destruction before it can infect cells. Second, by activating cytotoxic T cells (cellular immunity) that
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