This memo was provided to the NZ Ministry of Health on November 16th, 2022 in response to a request for rapid advice on November 15th, 2022. The memo presents results for specific scenarios of interest: case isolation of 7 days or 5 days with no test-to-release, and 5 days with test-to-release. The method and results used here are from a previously published, internally reviewed report.

Executive Summary

COVID-19 Modelling Aotearoa has been asked to provide guidance on the likely outcomes of changing case isolation settings in Aotearoa. We understand that the change being proposed is a shift from the requirement to isolate for 7 days (i.e. release on day 8) to the requirement to isolate for a minimum of 5 days and a maximum of 7 days, with possible early release on days 6 or 7 for individuals who have returned a single negative result on a Rapid Antigen Test (RAT).

  • In all cases day 0 is the earlier of the date of symptom onset or the date of first
    positive test result.
  • In the test-to-release (TTR) scenario, the earliest that an individual could be
    released from isolation would be on day 6 (i.e. isolating from day 0 to day 5), if
    they returned a negative RAT result on that day

We have used a stochastic simulation model to calculate average population-level case isolation outcomes for a range of metrics.