Public scanning of the NZ Covid Tracer app’s QR codes declined in the past week, harming its effectiveness for contact tracing as three new community cases in Auckland sent the city into 72 hours of level three lockdown on Sunday night.

With the rest of the country at level two, health authorities are scrambling to test potential close contacts and those who visited places at the same time as the three confirmed cases.

"After Waitangi Weekend, we saw QR code scan counts start to drop again as the pressure from the Northland case faded away,” Dr Andrew Chen, University of Auckland research fellow with Koi Tū: The Centre for Informed Futures told BusinessDesk this morning.

“At the current levels of scanning, I don't think the government can rely on it as a mitigating factor for the lack of information they have around the current cases in South Auckland. Other information will be more important, such as determining an epidemiological link to a source, and getting a high number of tests conducted to determine if there is community transmission."

Chen previously said daily app scans should total at least six million if every New Zealander possible was using the app. After a case of covid in the community in Northland was reported on Jan. 25 app scans hit over 1 million several days in a row. 

But in the three weeks from then until yesterday, in the absence of more cases or lockdowns, Ministry of Health data shows daily scanning has been sporadic with numbers falling significantly as people feel less threatened by the possibility of an outbreak.

The latest available data shows scans from 1pm on Saturday to 1pm on Sunday totalled 731,056, over 150,000 less than the 24-hour period prior. 

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The above chart shows daily app scans (red) against smartphones with the Bluetooth tracing feature active (grey). The regular dips in scan numbers are often around weekends, though the steady decline in overall scans reflects national complacency.

Contact tracing is most effective when there is an abundance of data in the weeks previous to a recorded new community case. 

While QR code scanning is manual and requires active participation from every Kiwi, the Bluetooth feature is automatic, so the active number of devices stays relatively constant as people pass each other in day-to-day situations.

Chen said the Bluetooth figures were encouraging despite the tardiness for manually scanning QR codes.

“If the usage keeps going up, then that may give the Ministry of Health more confidence that they can lower the alert levels because the app covers enough people. The best time to be scanning QR codes and having Bluetooth Tracing on is fourteen days before there are cases in the community – the second-best time is now."