SPR L13 Vaccinations and Immunotherapy 1 Flashcards
Learning Outcomes
- Approaches to control of infectious disease in populations
- The requirements for a good vaccine.
- Different types of vaccine and the advantages and disadvantages of these.
- The use of adjuvants.
- Current vaccines in use and describe the UK vaccination schedule
Control of Infectious Disease in Populations
How can infectious diseases be limited?
by drugs, immunisation and a ‘healthy’ environment
- By the use of drugs (chemotherapy).
- By vaccines (immunisation).
- By improving the environment (better sanitation, nutrition).
Control of disease
- What do decisions depend upon?
- What can then be determined?
- Give an example of how clinical observation is important
- How are surveillance systems set up?
- ability to recognise outbreaks of disease, follow their progress and identify the causative organism
- where and how outbreak has arisen, who is at risk and what treatment is necessary to control further infection
- e.g. discovery of AIDS in 1981 through increased occurrence of Pneumocystis jiroveci pneumonia.
- through government locally and through the World Health Organisation (WHO)- e.g currently swine flu.
Control Versus Eradication
Eradication is always the ideal endpoint - what questions need to be asked?
What are important factors in eradication and control?
- Which diseases could, with suitable effort, be eradicated?
- Would the cost of eradication be justified?
- Which diseases need urgent measures to stop them getting worse?
- Which diseases are responsible for the most human suffering and economic loss?
Important Factors Disease limited to humans host
- Cases easily recognized clinically
- Surveillance possible
- Stable, cheap, effective vaccine available
- Worldwide programme possible
- Eradication programme is cost-effective
To Control Infection Understanding the Biology of the Infectious Agent is Important
Hosts are 4 classes of individuals, name these
- susceptible;
- infected but latent (i.e. non-infectious);
- infected and infectious;
- recovered and immune
To Control Infection Understanding the Biology of the Infectious Agent is Important
Recovery from infection usually gives what?
What are the exceptions?
immunity against re-infection; in case of viral infections, this may be lifelong. –
Exceptions (e.g. herpes, HIV, RSV)
For macroparasites immunity is short-lived.
Incubation, Latent and Infectious Periods
- What is the incubation period?
- What is the latent period?
- he phase before symptoms appear
- overlaps with incubation period- is non-infectious phase
Why Important to Understand the Reproductive Rates of Micro-organisms and Parasites
- What does the initual rate of increase of an infection depend upon?
- What is RO?
- What is herd immunity?
- the magnitude of R0 (the basic reproductive rate).
- R0 is defined as the average number of secondary cases of infection produced by one primary case in a completely susceptible population. - The greater the value of R0 the greater the rate of increase.
Appearance of infections caused by organisms with a high R0 requires a rapid protective response at both the individual and community level. e.g. measles has a high R0 value (15-17).
- Concept of herd immunity – level of immunity at which an infectious agent can no longer continuously circulate is related to R0
The Effective Reproductive Rate-R
The spread of infection is related to R0 the basic reproductive rate of the infectious agent. However susceptibility differs with…?
- Sex
- Age
- Genetics
- Nutritional and immunological status
- Previous exposure;
Therefore a more actual reproductive rate is measured by the effective reproductive rate - symbol R.
Concept of herd immunity – level of immunity at which an infectious agent can no longer continuously circulate (R becomes <1)
Transmission Success
- What does this vary between? Why?
- Varies between communities because of differences in demography (net birth rate) and behavioural (patterns of mixing). e.g. inter-epidemic period for measles in large urban centres in Africa or India before the introduction of mass vaccination was often 1 year.
In the UK and the USA the period was typically 2 years.
Reflects difference in the average age at infection
Vaccination
What is vaccination used to do?
Vaccination is used to protect individuals
- Those exposed to infectious agents- in hospitals, laboratories etc
- Tourists or military personnel travelling to areas where they encounter unfamiliar and serious infections.
To control or eradicate disease
- The higher the rate of R0 the harder it will be to eradicate the infection. e.g. measles (R0 15-17) will be more difficult to eradicate than smallpox was (R0 2-4).
Mass Vaccination Can have Indirect Disease Consequences
What are these?
- Increases the average age at infection
- Increases the inter-epidemic period.
- Affects the age distribution of cases and the pattern of fluctuations.
The Risks of Infection Must Outweigh any Risk Associated with Vaccination
Give examples of the age-dependent risk of complications from infection
-
Mumps
- Vaccination reduces risk as complications increase with age- 20-30 year peak.
-
Measles (encephalitis)
- Vaccination reduces risk and CNS complication s increase with age
-
Rubella
- Vaccination can push the risk of rubella infection towards the child bearing years.
Means of infection Control in Populations other than Vaccines
Give examples of general measures that can be taken
- Water purification (water-borne diseases)
- Sewage disposal (enteric infections)
- Hygeine, crowding, safe sex,
- Animal reservoirs
- Improved nutrition (host defense)
- Improved housing (less crowding, dirt, etc.)
- Screening (antenatal, blood transfusion etc)
Means of infection Control in Populations other than Vaccines
Give examples of measures that can be taken in…
- Food
- Zoonoses and arthropod-transmitted infections
- Cold storage
Pasteurization (milk, etc.)
Food inspection (meat, etc.)
Adequate cooking
- Control of vectors (mosquitoes, ticks, lice, etc.) Control of reservoir animal (rabies, bovine TB)
Live Attenuated Vaccines
- Some of the attenuated virus vaccines in current use were produced by…
- What are the two principal methods?
- Oral polio vaccine (OPV), attenuation was by…?
- the selection of mutants induced at random - ‘genetic roulette’
- serial passage in cells cultured in vitro, adaptation to low temperatures.
- passage through monkey kidney cells or human embryo fibroblasts, virulence being checked for by signs of neurotoxicity in monkeys .
Analogous methods have been used for measles, rubella, mumps and yellow fever
