vaccination and public health Flashcards
Strategic aim of vaccines:
- selective protection of vulnerable
- eliminate disease
- eradicate disease
elimination vs eradication
elimination = reduce number of infections, trasmission to humans, prevent outbreaks
eradication = no other reservoirs of the infection exist in animals or environment
EX of elimination
tetanus, measles, diptheria
EX of eradication
smallpox, polio
Programmatic aim of vaccination:
- prevent deaths
- prevent infection
- prevent transmission
- prevent cases in certain groups
How do you select a ‘high-risk group’?
- Risk of exposure higher (e.g. healthcare workers)
- Consequence of infection is more severe
2 ex of passive immunity
- maternal antibodies
- injecting immunoglobulins
2 ex of active immunity
- natural infection
- vaccine
Why is active better than passive?
Lasts longer, immunological memory
R0 =
Basic reproductive number. Average number of individuals directly infected by an infectious case during the infectious period in a totally susceptible population
R0 is a property of…
Biological agent
R0 is proportionate to…
- length of time case is infectious
- number of contacts
- chance of transmitting per encounter
R =
effective reproductive number. Actual average number of secondary cases per primary case observed in a population
R0 is usually … than R
> . this is because pop isn’t 100% susceptible
In a homogeneous mixing population where s is the proportion susceptible R =
R = R0 x s
R > 1
increases number of cases
R = 1
epidemic threshold. stable
R < 1
decreasing number of cases
S* =
s* = 1/R0
Herd immunity threshold H =
H = 1-1/R0 or 1- S*
Herd immunity measures…
the indirect protection to the unvaccinated as well as direct effects of vaccination.
Why is herd immunity important?
<100% vaccine efficacy
<100% vaccine uptake.
Some people have contraindications
factors to consider when DECIDING and IMPLEMENTING a vaccine program:
- is the disease a public health problem?
- is immunisation the best strategy
- what will the net impact of a new vaccine be?
- possible negative effects
- additional resources
- impact on public perception
- const analysis
Ex of passive vaccine
tetanus gangrene snake bite hep B rabies Placental IgG Colostral IgA
Live vaccines
naturally attenuated or artificially attenuated
‘naturally attenuated’
a related strain or species (e.g. cowpox and smallpox)
EX of live vaccines
Oral polio, MMR, yellow fever, nasal influenza
Non-living vaccines
killed whole organisms, antigenic components
Advantages of dead/inactivated vaccines
- effective
- good stability in transport and storage
- safe for immunodeficient patients
- no risk for poliomyelitis
Disadvantages of dead/inactivated vaccines
- doesn’t incude gut immunity
- boosters required
- injection
- higher community vaccine levels required
Advantages of live/attenuated vaccines
- effective
- lifelong immunity
- induces immune response similar to natural infection
- indirect community immunisation
- oral
- boosters not required
Disadvantages of live vaccines
Vaccine-induced poliomyiltis
- spreat to contacts w/o consent
- unsafe for immunodeficient individuals