Compulsory COVID-19 contact-tracing apps: More evidence from New Zealand

By Bronwyn Howell

New Zealand has attracted much international interest during the COVID-19 pandemic for the apparent success of its virus elimination strategy, keeping infection and death rates low. However, this has come at the cost of the world’s most stringent lockdowns when community infections are detected, along with draconian border policies — even for New Zealand citizens.  

Unfortunately, the delta variant has proven too difficult for New Zealand’s much-lauded elimination strategy to mitigate. A single case detected in Auckland in August has mushroomed into widespread community-based infections. New cases continue to increase, mostly in Auckland, but are spreading out to adjacent regions with the current daily nationwide average approaching 200. Elimination has been abandoned in favor of containment, as observed in almost all other countries. When all health districts nationwide reach a 90 percent full vaccination rate of the eligible population over 16 years old, the country will transition from its existing lockdown system to a new “traffic light” system based on expected demands for local health care resources given the extent of community transmission in each relevant area.

At all traffic light colors (green, orange, and red), the restrictions on vaccinated individuals are far less onerous than those facing unvaccinated individuals. Key to moving to the new system is the availability of vaccination certificates (due late November). However, regardless of the traffic light color, it will be mandatory for all businesses and individuals to keep records of their activities using either the NZ COVID Tracer (NZCT) smartphone app or other systems (e.g., paper records). This continues a mandate from COVID-19 Response Minister Chris Hipkins (which became active on September 7) that obligates premises operators and function hosts to ensure individuals comply with the requirement to scan or share other personal information facilitating contact-tracing activities in the event of their premises being identified as a possible site of infection transmission.

NZCT differs from most other smartphone contact-tracing apps (e.g., Apple/Google’s Bluetooth app) because it requires users to scan QR codes when entering premises or public transport vehicles. Scanning is an onerous but visible activity, enabling verification that the activity has occurred. However, monitoring and enforcement is costly, so it relies mostly on individual self-motivation or peer pressure for scanning to take place. The most interesting feature of NZCT use when it was voluntary was the extent to which scanning was not being done by registered app users. To that end, it is interesting to observe how app usage has changed following the instruction mandating its use.

While over 3.3 million apps have been downloaded (approximately 66 percent of the population), on any given day prior to Hipkins’ September 7 mandate, on average fewer than 20 percent of the registered applications recorded a scan, although this increased when local infections were notified in August 2020 and February 2021 (Figure 1). The number of active devices on a given day increased immediately following the mandate, but still only around 35 percent of apps were observed to be scanning. This was lower than the peak in August 2020 when 50 percent of apps were active. The mandate has increased the number of app users taking scans, but many app users are still not scanning daily.

By contrast, the proportion of apps activating an optional Bluetooth feature has not fluctuated with infection outbreaks. This rose from 50 percent of registered apps to 68 percent, but the increase appears to coincide with local outbreaks (August 18, when risk of infection increased), not the September 7 application use mandate.

Scanning activity has certainly increased following the mandate — from 500,000 scans per day in early August to 2.5 million (but falling) in September (Figure 2). This appears to be triggered by the mandate and not increased infection risk; there was negligible increase when the August outbreak was identified.

Source: New Zealand Ministry of Health data

However, Figure 3 shows that the average number of scans per active app has not increased much following the mandate. Most of the additional scanning activity has come from inactive users becoming active. For the most part, active users scanned just under two codes per day on average (with negligible change despite local viral spread until the August 2021 outbreak, during which the most stringent lockdown curtailed most activity). Following the mandate, just 2.2 scans per active device were recorded. This suggests that even the most enthusiastic scanners don’t scan very much, and the mandate has not altered that.

It remains to be seen whether even these low levels of activity can be maintained as the “traffic light” system becomes embedded. However, as active devices and scan numbers are falling (albeit slower than before) it seems that despite Hipkins’ mandate, the high costs of scanning, monitoring, and enforcement will remain significant limits to the usage and ultimate success of NZCT.

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