Lecture 26: Control of infections Flashcards
Monday 2nd December 2024
What are the main aims of intervention of infection?
Control
Elimination
Eradication
Extinction
Control…
maintains the parasite population to an acceptable level
Elimination…
zero incidence in a defined geographical area (local eradication).
Eradication…
zero incidence worldwide
Extinction…
infectious agent no longer exists in nature or in lab.
What are the intervention options
- Preventing transmission
- Intervening after transmission (to prevent further transmission)
Preventing transmission…
- Mass (random) or targeted vaccination. e.g. smallpox
- by risk group e.g. childhood vaccines MMR
- Spatial vaccination, e.g ring vaccination - FMD
- Reduction in contact
- by handwashing, condom use, environmental sanitation
Intervening after transmission (to prevent further transmission)
- Infectiousness curtailment - tracing & isolation, or culling
- e.g. SARS, hospital MRSA (humans)
- FMD, BSE, avian influenza (animals)
Give the intervention equations
Re = S x c x p x D
Re = S x R0
S =
susceptible proportion
D =
duration infectious
c =
contact rate
p =
probability of transmission
c x p =
effective contact
What is the logic of interventions?
- Reduce number Susceptible
- Reduce time infectious (reduce D)
- Reduce contact (reduce c x p; isolation)
Where does vaccination move susceptibles?
directly into the Immune class
How many (much) should be vaccinated?
Pc = 1 - 1 / R0
What is Pc?
Pc is the (minimum) proportion of individuals you need to vaccinate
What is the long term strategy for controlling infectious disease?
Herd immunity
How many individuals in the general population need to be immunised for herd immunity to be effective?
75%
What is the proportion of the population that needs to be vaccinated dependant on?
R0
Is herd immuity reachable without intervention?
No. Active immunisation is required for herd immunity to be reached.
An infection spreads in a population and has sufficient replenishment of susceptibles – endemicity.
An infection spreads in a population and has sufficient replenishment of susceptibles – endemicity.
Partial immunity on an individual level
Partial immunity may be considered at the individual level – a partial immune response.