Report delivered 10 September 2021

As Aotearoa New Zealand, and specifically Auckland, responds to the ongoing outbreak of Covid-19 that began in August 2021, we seek to explain and explore how changes to Alert Level restrictions may impact on the network of interactions on which Covid-19 is spread.

By representing Aotearoa New Zealand as an interaction network, we can investigate how changes to patterns of interactions between individuals translate into structural network changes that affect potential transmission pathways.

We use the Populated Aotearoa Interaction Network (PAIN), a synthetic network representing Aotearoa New Zealand, to illustrate how moves such as changing Alert Levels can affect the number of interactions that individuals will share and the expected size of largest connected component in the network. This combines analysis of the empirical interaction network with some estimates from network science for the level of connectivity in the interaction network for different scenarios of interactions outside the home and workplace.

A key finding of this report is that only a small increase in the number of connections between individuals from different dwellings (an increase from around 10% to around 20% of the number expected at Alert Level 1) is sufficient to increase the size of the largest connected component of the population who could be reached though transmission by a factor of 15; from around 90,000 to over 1.4 million.