Executive summary

  • We simulate the late July/early August re-emergence and spread of Covid-19 in Aotearoa New Zealand.
  • We use a stochastic, individual-based network model of all ~5 million individuals in Aotearoa, and run simulations for a period of 30 days.
  • Based on these simulations, we calculate: the expected time to detection of the first case after initial seed cases; the number of cases at the time of detection; the time until detection of a first case outside of Auckland; and how the overall number of cases increases without intervention.
  • Our model includes interaction pathways, referred to as ‘contexts’ in the network, broken down into network ‘layers’ representing home, work, school, and community structure.
  • Each simulation starts from initial (seed) cases corresponding to the first detected re-emergence cases in August 2020.
  • We run 50 realisations of each simulation for 30 days – each simulation scenario corresponding to one of three different levels of transmission rate.
  • To model the behaviour of individuals in the weeks prior to the 11 August 2020 re-emergence, we assume a moderate rate of people getting tested if mildly symptomatic.
  • No contact tracing or intervention is present in this scenario, other than cases that test positive being isolated to their dwelling.