Lecture 25. Michael baker Flashcards
What are the most important pieces of information we need to know to “size up” a pandemic( assess the threat)
- How transmissible
- reproduction number, r0, reff - How severe and unequal
Cause fatality risk(CFR) and infection fatality risk(IFR)
Inequalities of pandemic and response - How controllable
- Available interventions and effectiveness
- Feasibility of response, sector capacity, public acceptability and adherence
- Economic assessment. cost of action/inaction - How certain is the information and how stable is the threat
• Availability & quality of information, experience/dogma
• Science capacity, ability to track threats & generate/test scenarios
• Stability of threat, evolution
What are the most important pieces of information we need to know to “size up” a pandemic( assess the threat)
- How transmissible
- reproduction number, r0, reff - How severe and unequal
Cause fatality risk(CFR) and infection fatality risk(IFR)
Inequalities of pandemic and response - How controllable
- Available interventions and effectiveness
- Feasibility of response, sector capacity, public acceptability and adherence
- Economic assessment. cost of action/inaction - How certain is the information and how stable is the threat
• Availability & quality of information, experience/dogma
• Science capacity, ability to track threats & generate/test scenarios
• Stability of threat, evolution
What are the main strategic options for responding
to a pandemic?
Control:
Mitigation(Reduce to avoid overwhelming the healthcare system)
or Suppression(Reduce to minimize negative health impacts )
Elimination: Reduce to zero in a country or region for prolonged
periods. –>Eradication: Reduce to zero at a global level permanently
eg SARS, Smallpox
Reproduction number
Basic reproductive number, R0 = mean number of infections directly generated by 1 case in a population where all individuals are susceptible to infection
Effective reproduction number, Reff or Rt = mean number of additional infections caused by an initial infection at a specific time,
The effective reproduction number can be estimated by the product of the basic reproductive number and the fraction of the host population that is susceptible (x). So: R = R0x
For example, if R0 for influenza is 12 in a population where half of the population is immune, the effective reproductive number for influenza is 12 x 0.5 = 6.
Why do we want to keep the reproduction number under one?
exponential growth above 1
What affects the reproduction number
- transmissibility (-> physical distancing, masks, ventilation, vaccination)
- contact rate( case isolation, contact quarantine, work, school from home)
- duration of infectivity(vaccination, antimicrobial treatment, immunomodulatory treatment)
Interventions try to reduce one or more of these qualities
Interventions for eliminations strategy:
- Exclusion of cases
• Keep it out – Border Management - Case and outbreak management
• Stamp it out – Testing, contact tracing, isolation/quarantine - Preventing community transmission
• Hygiene measures, masks
• Physical distancing & travel restrictions
• Vaccination - Social safety net
• Wage subsidy scheme & many other forms of support
Interventions for eliminations strategy:
- Exclusion of cases
• Keep it out – Border Management - Case and outbreak management
• Stamp it out – Testing, contact tracing, isolation/quarantine - Preventing community transmission
• Hygiene measures, masks
• Physical distancing & travel restrictions
• Vaccination - Social safety net
• Wage subsidy scheme & many other forms of support
What proportion of the population do we need to
vaccinate to achieve population protection/herd immunity
threshold?
Use the reproductive number to find out
the more transmissible- the higher % of the population needs to be vaccinated
1- (1/R0)
Why is reaching herd immunity hard?
vaccine effectiveness( eg 70% at 3 doses) x coverage( 50% triple vaxced)= 35% while the herd immunity threshold is 90%
How would you measure the success of your
pandemic response?
Decline in Cases Deaths Life expectancy impact Economy Freedom Equity( disease and vaccine coverage)- NZ did poorly in
How can we reduce the risk of people getting
Covid-19 within New Zealand, eg in health care settings?
- Host factors( age, vaccine, obesity, income)
- Environmental factors( crowded, close-contact, confined)
Hierarchy of controls
Elimination
Engineering controls- ventilation
Administrative controls- make people work from home
PPE( least effective)- masks
What affects the value of testing?
Prevalence( low- less value, high-more value)
Misinformation vs disinformation
Misinformation- false information
Disinformaiton- harmful, intentionally spreading false information, propaganda
Misinformation vs disinformation
Misinformation- false information
Disinformaiton- harmful, intentionally spreading false information, propaganda
lessons for improving public health
a) Improving evidence-informed decision-making (incl. crises)
b) Adapting responses to future threats (“All hazards”)
c) Building effective public health infrastructure
d) Supporting effective global health institutions
e) Seizing public health opportunities provided by the Covid-19 reset
