Only one in 10 Dudenites are using the COVID Tracer app when they're out and about, a "disturbingly low" percentage according to researchers.

And a third of venues aren't getting anyone to scan in at all, many of them bars - a high-risk setting for COVID-19 transmission if there was an outbreak. 

Researchers in the southern city randomly selected 40 locations - 10 cafes, 10 restaurants, 10 bars, five churches and five supermarkets - and watched for an hour at each as people came and went on different days in January and February.

At 12 of the 40 venues, no one scanned in at all - including eight of the 10 bars. Of the two bars that did have people scan, one had three out of 30, the other a single person out of six. The other places where no one scanned included a church with 37 visitors, two restaurants with 14 visitors between them and a cafe with 11 visitors. The median scan rate across all the venues was 10.2 percent.

The venues didn't do much better than their patrons. Half the bars, cafes and restaurants didn't display their QR codes properly, failing at least one of the six criteria (A4 size, prominent and near the main entrance, not on sliding or revolving doors, at least 130cm from the ground, unobstructed and not in high glare). 

All the supermarkets were in 100 percent compliance with the rules. 

"We observed low levels of QR code poster scanning at all of the selected venues, despite the Ministry of Health's 'Make summer unstoppable' campaign and frequent pleas from the Director-General of Health and the COVID-19 Response Minister for everyone to play their part and scan," the researchers wrote in the study, published on Friday in the New Zealand Medical Journal. 

"The low proportions of people who scanned QR code posters on entering the observed venues are concerning."

New Zealand's COVID Tracer app allows contact tracers to quickly find people who might have been exposed to the virus.

"If a non-scanning visitor to a venue was subsequently diagnosed with COVID-19, they might fail, or take some time, to recall that they had visited the venue or when they had visited, thereby hindering effective contact tracing and increasing the risk of onward community transmission," the study said.

"Second, even if a venue was rapidly identified as a 'location of interest', non-scanners who had visited at the same time as a case would learn of this later than those who had scanned because they would not receive a digital alert."

Usage nationwide spikes whenever there's an outbreak, and drops off over time. For example, after the small Auckland outbreak in mid-February, Ministry of Health data shows daily scans and active user numbers doubled overnight; both have since fallen by nearly 50 percent.

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The researchers expressed particular concern about bars, which in Dunedin - a student town - "are often crowded and behaviour may be influenced by alcohol"; and churches, which "have been associated with large clusters" in the past and frequented by many older people, who are at greater risk of serious illness or death if they contract the disease. 

The researchers said they didn't track how many people signed into venues manually or kept personal records; they also noted in a few cases couples would only have one person use the COVID Tracer app on behalf of them both.

They also noted many older people or the less well-off might not have phones new enough to run the app, raising a "disturbing paradox: digital solutions to facilitate contact tracing may be less likely to reach groups who are most at risk of severe COVID-19 outcomes, such as older people, those on low incomes, and those with comorbidities, including Māori and Pasifika".

Dunedin has not had a confirmed case of COVID-19 since April last year, raising concerns of complacency. 

"Beliefs that Dunedin is somehow safe from COVID-19 are worrying as they ignore the mobile nature of the population in New Zealand; for example, University of Otago students from Auckland were permitted to travel to Dunedin while Auckland was still at alert level 3 and thousands of students from all over the country recently arrived in Dunedin in time for the large social events associated with Orientation Week."

There has only been a single reported prosecution to date for not displaying a QR code.