Microbiology 8- Defence and vaccination against bacteria Flashcards
Properties of a Good Vaccine
Stimulates an effective immune response
Safe and does not cause adverse reactions
Inexpensive
Stable
Easy to administer
Simple for both manufacturer and regulatory authorities to control
Describe direct protection
Stopping the disease affecting you if you get the disease
Describe indirect protection
Stop transmissions
How do we determine vaccine Safety and Efficacy
Phase 1 trials
Primarily for safety but are often also used to assess immunogenicity
Usually small numbers of adults
Phase 2 trials
Primarily for assessing immune response but also used to expand safety database
Typically includes all groups that are likely to use the vaccine
Phase 3 trials
Protection studies, usually placebo controlled double blind trials
provide statistically conclusive data for licensure
Require good disease surveillance
case ascertainment
definition of endpoint
What is the definition of vaccine efficacy and what is the formula
The reduction in the incidence of disease among people who have received a vaccine compared to the incidence in unvaccinated people.
1-
Attack rate in vaccinated group /Attack rate in unvaccinated group
What is the definition of herd immunity and what is the formula
Form of immunity that occurs when the vaccination of a significant portion of the population provides a measure of protection for individuals who have not yet developed immunity.
1-
Attack rate unvaccinated post-introduction
Attack rate unvaccinated pre-introduction
What three elements do vaccines consist of?
Antigen
To stimulate immune response to the target disease
Adjuvant
To enhance and modulate the immune response
Excipients
Buffer, salts, saccharides and proteins to maintain the pH, osmolarity and stability of the vaccine
Preservative
Typical vaccine antigens
Live attenuated organisms
Killed whole organisms
Purified component vaccines
Toxoids
Polysaccharide conjugates
What does DTaP-Hib-IPV protect against
Tetanus and Diptheria Toxoids
Bordatella pertussis - whooping cough
Haemophilus influenzae type b
Inactivated polio virus types 1,2 and 3
How does DT vaccine work
chemical inactivation of bacterial exotoxin
What is whooping cough caused by
Bordetella pertussis which infects ciliated epithelium and releases toxin
What were some side effect of the whooping cough vaccine
anaphylaxis
prolonged crying
febrile siezures
What does hib cause and why is the vaccine effective
H. influenzae type b causes meningitis and septicaemia in the young.
Bacterial surface covered by a polyribosyl-ribitol phosphate capsule.
Polysaccharides are poorly immunogenic
The Hib component is a conjugate vaccine
What is a conjugate vaccines
Carbohydrate chemically linked to immunogenic protein.
T cell recognition of protein carriers enhances B cell activation
Promotes efficient antibody response to polysaccharide capsule
How do conjugate vaccine work
some bacteria have polysaccharide antigens and injecting them wouldn’t really stimulate a strong enough response because they’re not taken up by antigen presenting cells and presented because they’re not peptides so you dont get t cell immunity
if u inject the polysaccharide with a conjugate protein then it’ll be presented on APC and you get T cell immunity not just antibodies (and you’d only get IgM and IgD antibodies without T cell help anyway)
How do vaccines for group B meningococcal disease work
They target outer membrane vesicles which have all the same antigens as the bacteria
What are adjuvants?
They potentiate the immune response (humoral, cellular or both).
What are the two types of adjuvants
Delivery systems
Immune potentiators
4 strategies Pathogenic bacteria have to avoid host defences
Resist Complement
Having thick cell wall - Mycobacterium tuberculosis
Capsule - Neisseria meningitidis
Resist Antibodies
Antibody protease - Streptococcus pneumoniae
Antigenic variation - Neisseria gonorrhoeae
Resist Phagocytosis
Polysaccharide capsule - Neisseria meningitidis
Debilitate phagocytes - Yersinia pestis
Hide inside other cells - Chlamydia
Inhibit Intracellular Killing
Escape from phagosome - Listeria monocytogenes
Block phagosome maturation - Mycobacterium tuberculosis
