This document collates results and advice given to the NZ Ministry of Health in September 2022 as part of a rapid response to requests for modelling advice on consequences of removing case isolation.

Using the Network Contagion Model (NCM) we model the estimated relative change in the effective reproduction number (Rt) for COVID-19 in Aotearoa, for different scenarios of case isolation settings. We explore the effect of different levels of the “proportion of people taking action” when they test positive for COVID-19, and “how much people change their behaviour” when they test positive for COVID-19.

We find that many people isolating imperfectly, is preferable to a few people isolating perfectly but others not changing their behaviour at all. The strength of this effect is discussed with reference to the Addendum to this report (referenced below).

The finding in this report has obvious equity implications. Communities with more people who are less able to isolate, both within their dwelling (e.g. due to crowding within the home) and beyond their dwelling, (e.g. due economic pressures requiring them to return to work) will experience fewer protections and higher rates of transmission compared with those communities where a larger fraction of individuals are able to isolate when infected.
Providing support and clear messaging to enable (and encourage) people to isolate if they are infectious will remain important even if the legal requirement is removed.

This version of the report includes minor revisions following internal peer review, as well as reference to an Addendum where we present the findings of sensitivity testing of transmission within households during quarantine.

This report is the second of three related documents that use a similar method to consider the effect of these policy changes.