15 September 2021

We use a range of data sources and analytic approaches to estimate the number of movements between regions of Aotearoa and to give some estimates of the risk of transmission of COVID-19 to regions outside of Auckland, during the early stages of the August 2021 outbreak.

We also use one of these approaches – the Aotearoa Co-incidence Network – to generate some regional boundaries that are optimal for preventing inter-regional spread of COVID-19, in the sense that they partition the country into regions that minimise the potential spread between regions while maximising the number of links that are allowed to remain within regions.

We find that:

  • The regions at greatest risk of onward transmission from Auckland in the period before 17 August 2021 were Hamilton, Wellington, and Christchurch and their surrounding Territorial Authorities (TAs), along with Queenstown Lakes.
  • The movement-based risk assessment does not account for current epidemiological evidence, i.e. confirmed cases of COVID-19 in Wellington, but not in e.g. Christchurch.
  • Other than a brief initial surge of travel north from Auckland on 17 August 2021, there are very low levels of vehicle movements in or out of Auckland during the current AL4 intervention – similar to previous elevated alert levels. Similarly, traffic movements within Auckland are reduced to those seen in previous periods at AL4.
  • Potential interactions through work or education, in the period prior to 17 August 2021, for individuals living in those SA2s where cases of COVID-19 had been confirmed by 21 August 2021 extend beyond the Auckland region. Within Auckland, the pattern of SA2s with large numbers of potential interactions is heterogeneous and is widely spread, spatially.
  • It is possible to partition the country into regions with high numbers of connections through work or education within the region and low numbers of interaction between regions. Some possible partitionings are presented.