Microbiology 8 - Defence and Vaccination Against Bacteria Flashcards
What is direct protection in vaccine use?
This is preventing a healthy person being infected by vaccinating the individual.
What is indirect protection by use of vaccines?
Herd immunity - everyone is vaccinated in a population to isolate the disease, so that unvaccinated people are much less likely to come into contact with an infected individual.
What occurs in phase 1 trials of vaccines?
The vaccine is tested on a small number of adults to assess safety.
What happens in phase 2 trials of vaccines?
The immune response is assessed as well as safety - the people involved are those who are in target groups for the vaccine.
What happens in phase 3 trials of vaccines?
Protection studies are performed (often placebo controlled double blind trials). There must be statistically significant data generated, and disease surveillance must be accurate - clear endpoint.
What is efficacy?
The measure of a vaccines ability to offer protection.
What are effectiveness studies sometimes refered to as?
Phase 4 studies - they are less scientific, performed to convince users of the benefits.
How and when is vaccine efficacy calculated?
Calculated in phase III trials.
Vaccine efficacy = 1-(attack rate in vaccinated group/attack rate in unvaccinated group)
How is the vaccine coverage needed to achieve herd effect calculated?
(1-1/Ro (basic reproduction number))/effectiveness
How and when is herd effect determined?
Determined post vaccine introduction
Heard effect=1-(attack rate unvaccinated post-introduction)/attack rate unvaccinated pre-introduction
List the three components of vaccine formulations
Antigen, adjuvant and excipients
How do antigen vaccines work?
They stimulate the immune response to the target disease.
How do adjuvants in vaccines work?
They enhance and modulate the immune response. They may be delivery systems, which release antigen slowly (mineral salts/liposomes), or they may be immune potentiators (toxins, lipids, peptidoglycan, cytokines or hormones).
How do excipients in vaccines work?
They involve buffers, salts and proteins which maintain the pH, osmolarity and stability of a vaccine - may contain a preservative to prevent contamination if the same vial is used multiple times.
What is vaccinated against in the UK childhood immunisation programme?
- Rotavirus
- Meningitis B (hamophilus influenzae)
- Tetanus and diptheria toxoids
- Whooping cough
- Polio
What is the adjuvant present in paediatric combination vaccines?
Aluminium phosphate
Compare the use of aP and wP vaccines in whooping cough.
- aP is acellular, wP is whole cell
- wP is more effective, as patients that have the aP vaccine dont have a T lymphocyte response, so they dont clear the infection very fast and infected people can still transmit the pertussis.
How do conjugate vaccines work?
The antigen used is large and linear, so that it is not easily degraded. It contains a highly repetitive determinant. The immune response created mainly uses IgM, so has a poor memory effect and low avidity antibodies are produced. Therefore, repeated doses are required.
What do conjugate vaccines usually contain?
A weak antigen, such as a polysaccharide, is attached to a strong protein carrier to elicit a stronger immune response.
When are conjugate vaccines useful?
When humoral immunity is required. They reduce carriage and give a long lived, boostable immunity.
List some licensed conjugate vaccines.
- Pneumococcal conjugates (7/10/13 valent)
- Men C conjugates + men ACWY
- Geoup B strep (in the future)
What is serotype replacement?
Use of a vaccine with 10 out of 100 serotypes resukts in highly virulant serotypes increasing, compromising the vaccine use.
List some other bacterial vaccines.
- BCG is the TB vaccine
- Vivotif or Vipolysaccharide are used in typhoid vaccines
- Cholera vaccines (killed whole cell)
What do immunostimulatory adjuvant componants usually contain?
PAMPs, which are recognised by receptors on the innate immune system to cause cells to produce cytokines and influence the other cells in the immune system.
