The Government has put a dramatic drop-off in QR code scans down to an update to its NZ Covid Tracer app - but an expert suspects the bigger reason is complacency.
It comes as the Government has signalled that Bluetooth-enabled tracing tech could be rolled out as soon as November.
The August Auckland Covid-19 outbreak prompted a surge in people using the phone app to scan QR codes for contact tracing, rising from 30,659 to 1.1 million recorded scans within a week.
By the time the city moved out of lockdown, daily numbers had reached 1.7 million - and went on to hit a peak of 2.5 million on September 5.
But since then, numbers have been coming back down, falling to about two million on September 12, 1.5 million on September 20, 1.2 million on Saturday - and just over 975,000 on Monday.
Asked about the trend today, a Ministry of Health spokesperson cited an update to the app, rolled out on September 9, as a "significant factor" in the drop-off.
While the update made the app more user-friendly by removing the requirement to sign in before scanning, it also delayed the reporting of anonymised scan data to the ministry until users logged back into the app.
"This results in under-reporting of daily scans, which we are seeing reflected in the data," the spokesperson said.
"While we can't say for certain how much of the reduction is due to this technical issue, and how much is behavioural change as New Zealand moves to lower alert levels, we can confirm the underreporting issue will be resolved in the next app update."
But Dr Andrew Chen, a researcher at University of Auckland-based Koi Tū: The Centre for Informed Futures, believed the key reason was fewer people were bothering to check in.
"While I agree that this technical issue would contribute to the decline in scan counts, I think that the majority of it would be explained by fewer people participating."
Chen said that, with three weeks since the update was released, there should have should have been enough time for the data to "catch up" and recover from the initial effect on reporting - yet the numbers had kept falling.
Another indication could be found in population-level statistics, which suggested that if a person left home and scanned QR codes, they scanned about 2.2 to 2.3 codes each day at alert level 2.5 or lower.
Although it wasn't possible to divide the daily scan count by 2.2 to 2.3 to get the number of active users - because not everyone went out - Chen said that still pointed to a sizeable chunk of the app's 2.2 million registered users not scanning.
"Obviously some people scan more codes, some people scan fewer. The data also tells us that the daily scan count is dropping because there are fewer people participating each day, not because the same number of people are scanning fewer codes each."
"I think it's safe to say the majority of people aren't doing it."
Chen said he'd also seen ministry data, that wasn't publicly available, which showed fewer people engaging with the app in some way each day.
"So it's not just that people are becoming less mobile, or something like that - it's fewer people participating in the system."
With more people likely to be moving around the country over the school holidays, Chen said it was especially important that people used the app as often as possible.
That was critical in being able to give contact tracing services a 14-day log of personal movement.
Just as importantly, it allowed tracers to track down others who might have been exposed to the virus, and having a log also meant they could match up cases, and potential transmission, where check-ins overlapped.
A case in point was one Covid-19 case - and also a prolific app user - who took a chartered flight after coming out of managed isolation in Christchurch.
That meant tracers were given a head start on identifying and isolating close contacts, and were able to quickly issue exposure notifications in a number of places the person visited.
The ministry planned to launch a renewed marketing campaign over coming weeks encouraging Kiwis to keep scanning.
"The ministry encourages all New Zealanders to refresh their login when prompted and keep checking in with the app everywhere they go," the spokesperson said.
"This applies whether you are travelling or staying local, no matter what the alert level or gathering size, so we can quickly let people know when they may have been exposed to Covid-19."
Meanwhile, the ministry expected to have results of trials piloting new Bluetooth tracing tech at the end of October.
If successful, Bluetooth could be incorporated within the app, or more broadly, during November.
But the spokesperson said Bluetooth wouldn't replace QR codes - and it would still be important for app users to scan them.
"This is because Bluetooth would track person-to-person interactions while QR codes track visits to locations, both of which can be sources of transmission for Covid-19, and because Bluetooth will not detect interactions with people who don't use the app."