Vaccines Students PDF

Vaccines Senior Pathologist Department of Medical Microbiology National Health Laboratory Service & University of KwaZulu-Natal Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae ...

Vaccines Senior Pathologist Department of Medical Microbiology National Health Laboratory Service & University of KwaZulu-Natal Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae  Introduction Fundamentals of Vaccine Immunology DEFINITIONS Antigen  Molecules recognised by receptors on lymphocytes  These receptors recognize only a small part of a complex antigen referred to as the antigenic epitope Immunogen  Antigens that elicit the immune responses Adjuvant  Substance that non-specifically enhances antigen- specific immunity.  Introduction Fundamentals of Vaccine Immunology Components of the immune system: To establish infection , the pathogen must first overcome numerous surface barriers Any organism that breaks through the barrier will encounter  Innate immune response  Acquired immune response The two systems continually interact with each other to provide an effective immune response.  Introduction Fundamentals of Vaccine Immunology Pattern recognition receptors (PRRs) Found in all the membranes of the cells in the innate immune system Not specific for any given pathogen or antigen Bind to molecules associated with pathogens, called pathogen associated molecular patterns (PAMPs)  Introduction Fundamentals of Vaccine Immunology Pathogen associated molecular patterns (PAMPs) Present in large groups of microorganisms. Produced only by microbial pathogens Usually essential for the survival or pathogenicity of microorganisms Usually shared by entire classes of pathogens Recognition of PAMPs by PRRs leads to immune system activation Examples of PAMPs: Lipopolysaccharides (endotoxin), Peptidoglycan (cell walls), Lipoproteins (bacterial capsules), Hypomethylated DNA (CpG found in bacteria and parasites), Double-stranded DNA (viruses), Glucans, Flagellin (bacterial flagella  Introduction Fundamentals of Vaccine Immunology Antigen presenting cells (APCs) The innate and adaptive immune systems are principally bridged by the action of specialised antigen presenting cells (APC). Component of innate immunity Macrophages, B cells, dendritic cells  Introduction Fundamentals of Vaccine Immunology Antigen presenting cells (APCs): T cell receptor (TCR), recognizes foreign antigens only when they are bound to major histocompatibility complex (MHC) molecules. MHC: expressed on the cell surface of host cells APCs migrate to the local draining lymph node, stimulate T cells Activated T cells: CD4 or T helper cells:  Secrete cytokines: augment the capacity of other immune cells to perform their tasks  Introduction Fundamentals of Vaccine Immunology The adaptive immune response is composed of two arms: 1. B–cells: Produced in the bone marrow  Antibody mediated (Humoral) immunity 2. T-cells: Produced in the boner marrow, mature in the thymus  Cell mediated immunity  Introduction Fundamentals of Vaccine Immunology B cells : T cell-independent response Can directly bind to molecules expressed by pathogens (e.g. carbohydrates), with no need for previous internalisation and presentation by APCs. Antigen encounter, proliferate and differentiate into plasma cells: Plasma cells: Secrete large amounts of antibody Antibody: Released in the blood and other body fluids: Fight infection at distant sites Low-affinity antibodies of IgM type. Weaker immune response and the induction of memory is weaker than with T-helper cell activation  Introduction Fundamentals of Vaccine Immunology B cells T cell mediated immune response: Goal of immunization Due to simultaneous stimulation of both B and T cells by the same pathogen. Better immune response and more effective memory  Introduction: Fundamentals of Vaccine Immunology Binding of the antigen B–cell receptor and secondary signaling from cytokines released by T-helper cells B–cells begin somatic hypermutation Mature into a plasma cells: Production of antibody Isotype switching Proliferation and differentiation  Introduction Fundamentals of Vaccine Immunology Fundamentals of Vaccine Immunology IgM is the first antibody produced As the immune response progresses, the activated plasma cells will begin producing IgG specific to the particular antigen. Although IgM: much larger antibody IgG is a better neutralizing antibody. IgG binds more effectively to the antigen - the most important antibody for vaccines is IgG  Introduction Fundamentals of Vaccine Immunology IMMUNOLOGICAL MEMORY: Rapid proliferation Cells expressing receptors for the incoming antigen Effector cells Memory cells The adaptive response on secondary exposure leads to a rapid expansion and differentiation of memory T and B cells into effector cells, and the production of high levels of antibodies.  Introduction Fundamentals of Vaccine Innate Immune Immunology Advanced Immune system system First line of defence Second line of defence Not specific Specific Recognises conserved Recognise specific pathogen associated antigen molecular patterns Response delayed: Immediate response (responds to a pathogen Responses occur to the only after it has been same extent however recognized by the innate many times the immune system) infectious agent is Responses improve on encountered repeated exposure to a No memory given infection Memory present Stimulation of immunity by vaccines: Summary The body detects the threat: pathogenic agent or an immunization. Initial detection - done by the innate immune system; although, B-cells may also perform this function. The immune system recognizes epitopes on antigens. APC: engulfment by antigen-presenting cells. APC: process the antigens and insert the processed antigen along with the MHC protein onto the surface on the APC Activation of T helper cells: Activation and differentiation of B cells Effector functions and memory cells  Concept of vaccination Deliberate exposure to a harmless version of a pathogen generates memory cells but not the pathologic sequelae of the infectious agent itself. The immune system is primed to mount a secondary immune response with strong and immediate protection should the pathogenic version of the microorganism be encountered in the future Humoral responses are specifically enhanced upon re-exposure to the same (priming) antigen. This secondary response shows memory to the initial antigen. Most effective method for disease prevention The initial, primary response is relatively slow and low level. On subsequent immunization, the response is faster and of greater magnitude. Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae  Types of Vaccine Whole vaccines:  Live attenuated  Killed/inactivated Fractional vaccines  Subunit  Toxoid  Polysaccharide: Pure polysaccharide and conjugate polyssacharide  Recombinant New Vaccines: Nucleic acid vaccines and vector based vaccines  Whole vaccines: Live attenuated vaccines Virulent pathogenic organisms are treated to become attenuated and avirulent but antigenic. They have lost their capacity to induce full- blown disease but retain their immunogenicity. Selection of less or non pathogenic variants Replicate and disseminate to their target tissue in a pattern similar to that occurring during a natural infection Stimulate an effective and long-lasting immunity Does not require multiple doses Live attenuated vaccines: Limitations Very fragile (cold chain) Mutation to pathogenicity Live attenuated vaccines should not be administered to persons with suppressed immune response High reactogenicity e.g. whole-cell pertussis vaccine Examples of live attenuated vaccines:  Viruses: Oral polio; measles, mumps, rubella (MMR)  Bacteria: BCG  Killed pathogen - heat or formalin Organisms are killed or inactivated by heat or chemicals but remain antigenic. Usually safe but less effective than live attenuated vaccines: Booster doses may be needed to maintain long-term immunity Relatively stable over time, better resistance to cold chain deviation The only absolute contraindication to their administration is a severe local or general reaction to a previous dose. Examples: Inactivated polio vaccine  Subunit vaccines Only epitopes of immunologic interest Advantages:  Chemically defined , stable and safe free of unnecessary components, less side effects  Safer in viruses that are oncogenic or establish latent infection  Feasible even if virus cannot be cultivated  Relatively cheap to manufacture  Changes to natural variation of the virus can be readily accommodated Subunit vaccines Disadvantages: Not as immunogenic , may require carrier protein molecule/adjuvant Requires primary course of injections followed by boosters Examples: acellular pertussis  Toxoid Vaccines Some bacterial diseases are caused by a toxin Prepared by detoxifying the exotoxins of some bacteria Adjuvant (e.g. aluminium precipitation) is used to increase the potency of vaccine. The antibodies produced in the body as a consequence of toxoid administration neutralize the toxic moiety Highly efficacious and safe immunizing agents. Examples: Diphtheria, Tetanus  Polysaccharide vaccines Unique type of inactivated subunit vaccine composed of long chains of sugar molecules that make up the surface capsule of certain bacteria  Pure polysaccharide  Conjugate polysaccharide  Polysaccharide vaccines: Pure polysaccharide T-cell independent: able to stimulate B cells without the assistance of T-helper cells. Inability to induce immune memory: revaccination every few years is also needed regardless of age. Repeat doses of polysaccharide vaccines usually do not cause a booster response Antibody induced with polysaccharide vaccines has less functional activity than that induced by protein antigens. Predominant antibody produced is IgM, and little IgG is produced. Not consistently immunogenic in children younger than 2 years of age Polysaccharide vaccines: Conjugate polysaccharide Polysaccharide antigen coupled with Proteins Proteins used as conjugate carriers include tetanus and diphtheria toxoids T cell dependent immune response: B cell help from T cells Activation of T cells and high affinity antibodies against polysaccharide Development of memory B cells specific for the polysaccharide antigen: long-term immune protection Examples: Haemophilus influenzae, Streptococcus pneumoniae  Recombinant vaccines DNA sequence coding for the antigenic protein is inserted into an expression system that is then able to produce large quantities of that specific antigen in vitro Purified or genetically engineered structural component of a pathogen Include only epitopes Their efficacy and safety also appear to be high Hepatitis B and human papillomavirus vaccines  New Vaccines: Nucleic acid vaccines and vector based vaccines Nucleic acid vaccines Genetic material from the pathogen to stimulate an immune response against it. Genetic material (DNA or RNA) is inserted into host cells →, read by the cell’s own protein- making machinery →produce antigens →trigger an immune response. So far: None approved for human use  New Vaccines: Nucleic acid vaccines and vector based vaccines Viral vector-based vaccines Modified virus (the vector) to deliver genetic code for antigen Use the body’s own cells to produce antigen Mimics what happens during natural infection Triggering a strong immune response Previous exposure to the vector could reduce effectiveness  Types of Vaccines Live Live Killed Toxoids Cellular fraction Recombinant vaccines Attenuate Inactivated vaccines vaccines d vaccines vaccines Small pox BCG Typhoid Diphtheria Meningococcal Hepatitis B variola Typhoid Cholera Tetanus polysaccharide vaccine vaccine oral Pertussis vaccine Plague Plague Pneumococcal Oral polysaccharide Rabies vaccine polio Salk polio Yellow Intra- fever muscular Measles influenza Mumps Japanise Rubella encephalitis Intranasal Influenza Typhus Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae Route of administration Deep subcutaneous or intramuscular route (most vaccines) Oral route (sabine vaccine) Intradermal route (BCG vaccine) Scarification (small pox vaccine) Intranasal route (live attenuated influenza vaccine) Adjuvants Subunit vaccines, do not contain sufficient natural adjuvant To improve immunogenicity. Provide the PAMPs required to drive the innate immune system to release danger signals to drive antibody and T-cell responses Liberation of antigen, chemoattraction, and inflammation Most widely used are aluminum salts (mainly hydroxide or phosphate) Scheme of immunization Primary Booster Cold Chain The "cold chain" is a system of storage and transport of vaccines at low temperature from the manufacturer to the actual vaccination site. The cold chain system is necessary because vaccine failure may occur due to failure to store and transport under strict temperature controls Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae  Bordetella Small, Gram-negative coccobacilli Cause respiratory tract infections Contains eight species  Major species Bordetella pertussis: Whooping cough  Bordetella parapertussis: Similar disease as B. pertussiss but mild because it does not produce pertussis toxin  Bordetella pertussis: Microbiology Obligatory aerobic Growth at 35-37 Special growth requirements:  Charcoal or blood: protect from inhibitory substances found in growth media Slow growth: 2-4 days Bordetella pertussis: Virulence Factors Structural: Mediate adhesion to respiratory tract  Filamentous hemagglutinin  Fimbriae  Pertactin Secreted:  Pertussis toxin  Adenylate cyclase toxin  Tracheal toxin Bordetella pertussis: Virulence Factors Secreted Pertussis toxin  Major virulence factor  Only produced by this species  Locally: Adhesion to respiratory tract  Systemically: Absorbed into systemic circulation-responsible for many clinical features of pertussis  Component of vaccine Bordetella pertussis: Virulence Factors Other toxins:  Tracheal cytotoxic: Damages ciliated epithelial cells of the airways  Adenylate cyclase toxin: Inhibit chemotaxis and phagocytosis Bordetella pertussis: Epidemiology Found exclusively in humans Cause disease only in humans Highly contagious and spread by airborne droplets High attack rate: 90% Epidemic cycles: 3-5 years Unvaccinated: common in children 1-5 years Vaccinated: common in children < 1 year, adults Most severe disease in infants Atypical (Mild) presentation in vaccinated individuals but source of transmission Bordetella pertussis: Clinical Features Whooping cough: 3 stages (overlapping) 1. Prodromal/catarrhal stage: 5-10 days after acquisition  Non-specific cold or flu symptoms: Rhinorrhoea, malaise, fever, sneezing, and anorexia  Highly contagious: High number of organisms in the URT  Appearance of cough later  Lasts 1-2 weeks Bordetella pertussis: Clinical Features 2. Paroxysmal stage  Pathognomonic signs: Last for weeks: Paroxysmal cough, whoop and posttussive vomiting Paroxysmal cough: up to 50 times per day Whoop: prolonged inspiratory at the end of cough: due to inspiration through swollen, narrow glottis Vomiting  Lymphocytosis  May results in: exhaustion, cyanosis, apnoea: ventilation may be required Bordetella pertussis: Clinical Features 3. Convalescence stage:  Occurs within 4 weeks of onset  Decrease in frequency and severity of coughing spells Bordetella pertussis: Clinical Features May be atypical:  Previously immunised older children and adults  Mild illness  Persistent cough Bordetella pertussis: Clinical Features Complications:  Secondary bacterial infection causing pneumonia  Atelectasis  CNS: convulsions, encephalopathy  Subconjuctival haemorrhages, inguinal hernia, rectal prolapse Morbidity and mortality higher in infants than other age groups Bordetella pertussis: Immunity Follows natural infection or vaccination Wanes after 5-12 years Acellular vaccine: contains purified virulence factors  Less side effects than original whole cell vaccine  All contain PT  Given along with diphtheria and tetanus vaccines Bordetella pertussis: Laboratory diagnosis Specimens: Nasopharyngeal aspirate or swab Better yield earlier in the disease Transport media: Regan-Lowe Bordetella pertussis: Laboratory diagnosis PCR: Test of choice  Sensitive and specific  Positive for longer period Culture:  Special media: Charcoal and blood, plus antibiotics  Growth in 2-4 days  Specific  Provide organism for drug susceptibility testing Bordetella pertussis: Treatment Antibiotic susceptibility testing not done routinely Resistance rare Treatment of choice: Macrolides Other options: trimethoprim sulfamethoxazole, Fluoroquinolones (adults only) Outline Introduction: Fundamentals of vaccine immunology Types of vaccines Application Bordetella pertussis Corynaebacterium diphtheriae  Corynebacterium diphtheriae: Diphtheria from the Greek word which means "leather hide". Small, pleomorphic aerobic and facultative Gram- positive rods. The cells tend to have clubbed ends and often remain attached after division, forming “Chinese letter” or palisade arrangements Corynebacterium diphtheriae Humans are the only natural hosts of C. diphtheriae Spread by respiratory droplets or direct contact Disease due to diphtheria toxin:  Released locally and absorbed systemically  Inhibit protein synthesis in affected cells  C. ulcerans and C. pseudotuberculosis may also produce toxin  Corynebacterium diphtheriae: Clinical manifestations: Local Incubation period: 2-7 days Respiratory: Multiplication in the pharynx: Fibrin, inflammatory cells: pseudomembrane. Can block the airway Corynebacterium diphtheriae: Clinical manifestations: Local Associated Cutaneous: cervical adenitis : Ecthyma “bull neck” diphtheriticum appearance Corynebacterium diphtheria: Systemic Various organs especially heart and nervous system:  Myocardiopathy  Neuropathy Complications: paralysis of diaphragm, cardiac failure Less complications from cutaneous diphtheria  Corynebacterium diphtheriae: Management 1. Antibiotics and antitoxin 2. Supportive treatment where needed 3. Laboratory diagnosis 4. Place in isolation 5. Notify: Public health interventions 6. Immunisation Corynebacterium diphtheriae: Antibiotics and anti-toxin Antitoxin:  Produced in horses  Neutralize circulating (unbound) toxin, will not neutralize toxin already fixed to tissues: prevent progression of disease. Antibiotics  Eliminate the organism and prevent spread  DOC: Penicillin  Alternative: erythromycin Corynebacterium diphtheriae: Laboratory diagnosis Complementary to clinical diagnosis All specimens should be collected before antibiotic treatment is started Clinician must inform the laboratory Specimens: Throat swabs (beneath membrane), wound swabs Culture:  Isolation of organism  Demonstrate toxin production  Corynebacterium diphtheriae: Management Isolate the Patient  Institute precautions appropriate for droplet borne infection and/or direct contact measures: side room with use of gloves, apron and surgical mask.  Continue isolation until two cultures from the nasopharyngeal and throat (or skin lesions if cutaneous diphtheria) taken at least 24 hours apart and more than 24 hours after completing antibiotics are negative for toxigenic C. diphtheriae, C. ulcerans or C. pseudotuberculosis Corynebacterium diphtheriae Notify relevant Health authorities Notifiable condition in South Africa Public health: infection control nurses and district and provincial communicable disease control Close contacts: Culture, antibiotic prophylaxis, vaccination Corynebacterium diphtheriae Immunization Clinical Disease: does not induce protective levels of immunity Cases should be immunised once they are clinically stable Vaccine: Diphtheria toxoid