18 October 2021

Using the FluTracking survey data for 2021 up until the week ending 29 August 2021, we can estimate the weekly incidence (new onset) of COVID-19-like symptoms within different age groups and different parts of the country. We use this to produce an estimate of the newly symptomatic population, and combine this with current testing data (up until 1 September 2021) to estimate how many people with new onset of symptoms (in the past seven days) would have been tested for COVID-19 through time.

  • Weekly incidence rates for any two or more COVID-19-like symptoms (CLI2+) in the week ending 29 August, 2021 was 6.7% for under 5s, 3.1% for 5-19 year olds, 3.3% for 20-64 year olds, 1.9% for 65+.
  • Weekly incidence rates for any one or more COVID-19-like symptoms (CLI1+) in the week ending 29 August, 2021 was 7.1% for under 5s, 4.8% for 5-19 year olds, 5.7% for 20-64 year olds, 3% for 65+.
  • New onset of illness, especially among pre-school and school age children has seen a large drop. This matches the declines seen in earlier Alert Level changes when schools were closed (Alert Level 3 and 4).
  • Despite the drop in testing seen in many regions, the lower incidence of illness still produces high symptomatic testing rate estimates in Auckland Region DHBs across all age bands except under 5s. A number of the approaches used to calculate this find testing rates up to 100%.

These estimates have a number of caveats. First, we are assuming that the weekly incidence (new onset of symptoms) estimated from the FluTracking survey is representative across a number of different communities. Secondly, we assume that all tests without an entry in the National Contact Tracing System (NCTS) database are seeking a test due to COVID-like symptoms. Finally, we assume that people seeking tests for symptoms would have had new onset of symptoms within the past seven days (although we test the sensitivity to this last assumption in section 3.2.2). In future it would be worth using more detailed information on the reason for seeking a test, including the symptoms people seek tests for, and the time from symptom onset to seeking a test. Unfortunately this data is not available yet.