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
