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. 2021 Nov 4;39(51):7429–7440. doi: 10.1016/j.vaccine.2021.10.079

Table 1.

Summary of data sources, assumptions, and prior distributions for a Bayesian network to assess risks versus benefits of the AstraZeneca COVID-19 vaccine.

Model inputs Data sources, assumptions, rationale Reference
Age distribution of infections from delta variant NSW COVID-19 case data from 1/6/2021 to 13/8/2021 were used to provide estimates of age distribution of infections from delta variant. Case data published daily by NSW Health, for the following age categories: 0–19, 5-year age groups from 20 to 69 years, and 70 + . For cases in the 0–19 age group, assumed that 40% were aged 0–9, and 60% aged 10–19 (based on age distribution of cases reported by NNDSS). Date range used was selected to reflect the first 6 weeks of delta outbreak, when vaccination coverage was relatively low. No significant change in age distribution of cases to 29/8/2021. See Appendix A, Table A1. [15], [34]
Age distribution of infections from alpha/wild variants COVID-19 cases reported in Australia from January to December 2020 were used to provide estimates of age distribution from alpha/wild variants. Data sourced from National Notifiable Diseases Surveillance System. See Appendix A, Table A2. [15], [35]
Case fatality rates of COVID-19 cases COVID-19 cases reported in Australia from January 2020 to 13/8/2021 were used to provide estimates of age-specific case fatality. Data sourced from National Notifiable Diseases Surveillance System. See Appendix A, Table A3. [15], [35]
Community transmission levels Chance of infection over 6 months calculated for different levels of community transmission. See Appendix A, Table A4.
Definitions of low, medium, and high transmission as defined by ATAGI document ‘Weighing up the potential benefits and risk of harm from COVID-19 Vaccine AstraZeneca’. Low – similar to first wave in Australia (equivalent to 0.05% of population infected over 6 months). Medium – similar to second wave in VIC in 2020 (equivalent to 0.045% of population infected over 6 months). High – similar to Europe in January 2021 (equivalent to 5.76% of population infected over 6 months).
Also included transmission scenarios equivalent to: zero transmission; 1% and 2% chance of infection over 6 months; 200 cases/day and 1000 cases/day in NSW; 1000 cases/day in VIC; 1000 cases/day in QLD. Other transmission levels can be added to model.		 [16]
Chance of infection by age group Chance of infection differed between age groups and by variants. Calculated chance of infection by age group if overall community transmission of 1%. Calculations based on age distribution of infections from delta and alpha/wild variants, and age distribution of Australian population. See Appendix A, Table A5.
Vaccine effectiveness against symptomatic infection Delta variant (ATAGI recommended data used in Doherty transmission model):
  • •

    33% effective after 1st dose

  • •

    61% effective after 2nd dose

(Note: Public Health England estimates effectiveness of 45% after 1st dose, and 70% after 2nd dose)
Alpha variant (from Vaccine effectiveness Expert Panel, Public Health England):
  • •

    60% effective after 1st dose

  • •

    80% effective after 2nd dose

 [5], [36]
Vaccine effectiveness against death Delta variant (ATAGI recommended data used in Doherty transmission model):
  • •

    69% effective after 1st dose

  • •

    90% effective after 2nd dose

(Note: Public Health England estimates effectiveness of 80% after 1st dose, and 95% after 2nd dose).
Alpha variant (from Vaccine effectiveness Expert Panel, Public Health England):
  • •

    80% effective after 1st dose

  • •

    95% effective after 2nd dose

 [5], [36]
Thrombosis and Thromobcytopenia Syndrome (TTS) after AZ vaccine Model uses data reported by ATAGI update following weekly COVID-19 meeting on 25/8/2021.Estimated rate per 100,000 1st dose of AZ vaccinations:
  • •

    Age < 50: 2.5

  • •

    Age 50–59: 2.7

  • •

    Age 60–69: 1.6

  • •

    Age 70–79: 2.1

  • •

    Age ≥ 80: 1.6

  • •

    For age ≥ 70 in model, used rate of 1.85 (average of rates for 70–79 and ≥ 80).

Estimated rate per 100,000 after 2nd dose of AZ vaccinations: 0.18 per 100,000 (no age specific rates available).
Case fatality rate in Australia ∼ 5% (noting that higher rates reported in UK ∼ 18%).
For sensitivity analysis, data from ATAGI reports on 1/9/2021, 8/9/2021, and 15/9/2021 were used.		 [37]
Background rates of atypical venous thrombotic disorders Background rates (in population not infected with and not vaccinated for COVID-19) of atypical venous thrombotic disorder (CVST and PVT) over 6 weeks were calculated for each age group to provide a comparison with chance of TTS after AZ vaccine.
CVST data from Kristoffersen et al.
  • •
    Age-specific rates per million population per year:
    • o
      Age < 20: 10.8
    • o
      Age 20–49: 18.0
    • o
      Age 50–69: 21.1
    • o
      Age ≥ 70: 20.7
  • •

    Case fatality of 7% for all age groups.

  • •

    Assumed equal rates in males and females.

PVT data from Ageno et al. and Søgaard et al.
  • •
    Age-specific rates per million population per year:
    • o
      Age < 20: 0
    • o
      Age 20–29: 5.5
    • o
      Age 30–39: 7.25
    • o
      Age 40–49: 15.75
    • o
      Age 50–59: 25.5
    • o
      Age 60–69: 49.5
    • o
      Age ≥ 70: 55.125
  • •

    Case fatality of 27.2% for all age groups.

  • •

    Assumed equal rates in males and females.

 [28], [29], [30]
Atypical venous thrombotic disorders associated with COVID-19 infection Rates of CVST and PVT in COVID-19 cases from a retrospective cohort study using data primarily from the USA.CVT:
  • •
    Cases per million COVID-19 infections:
    • o
      Male: 28.87
    • o
      Female: 54.20
  • •

    Case fatality 17.4% for both sexes.

  • •

    Assumed same rates for all age groups.

PVT:
  • •
    Cases per million COVID-19 infections:
    • o
      Male: 483
    • o
      Female: 318
  • •

    Case fatality 19.9% for both sexes.

  • •

    Assumed same rates for all age groups.

 [32]
Prior distributions* Assumptions Reference
Age distribution of Australian population Australian Bureau of Statistics. National population estimates, December 2020. See Appendix A, Table A6. [38]
Sex distribution of Australian population 50% male, 50% female
Variants 90% delta, 10% alpha/wild
Vaccine coverage 70% received 1st dose, 35% received 2nd dose

ATAGI = Australian Technical Advisory Group on Immunisation; CVST = Cerebral venous sinus thrombosis; PVT = Portal vein thrombosis.

*

Note that prior distributions do not affect results of scenario analysis but enables the model to provide population-level estimates. Assumptions can be changed as the situation evolves.