Use of the Covid-19 Tracer app has been dropping since March and preliminary data suggests daily QR scanning is only between 3-5 percent of the ideal level.
The government yesterday signalled it may mandate its use at alert levels 2 and 3.
Public health professor Nick Wilson said government action on this was overdue - with experts long advocating for it - because the current level of scans per day was inadequate.
A University of Otago Wellington team have been analysing mask use and QR code scanning on buses, with preliminary data showing QR scanning appears to be well under 5 percent and about 20 percent to 30 percent of commuters not wearing masks.
"This is concerning because buses are often relatively crowded environments and there is documented spread of the pandemic virus on buses internationally," Wilson said.
"If all 3.7 million adults in NZ were scanning there would perhaps be 11 to 22 million scans per day being registered. So perhaps the current level of daily scanning is only 3 percent to 5 percent of the ideal level."
Low use of the app would make it difficult to control an outbreak, especially with the more infectious Delta variant, he said.
Although the nature of the Delta variant means any outbreak of it would likely grow quickly, and make contact tracing more difficult for health authorities, he said.
"The mistake that was made in NSW was to rely too much on contract tracing … and not do more to use additional strategies," he said.
Wilson suggested the government should implement digital tracking when the time comes for travellers to isolate at home.
Sir David Skegg, who chaired the Covid-19 Public Health Advisory Group, told Nine to Noon the adherence to QR scanning "is just abysmal in this country".
"I walk into the shops, library, and supermarket, and I hardly see anyone else do it."
He backed making it mandatory at nightclubs, bars and churches which he said often ended up being at the centre of super spreader events.
On the other hand, he said the group had not recommended wider requirements for mask use.
"We will need to respond when we get outbreaks, as we will get outbreaks, we all need to be ready to wear masks much more consistently."
A Ministry of Health spokesperson said there had in fact been sustained increases in QR scans during and after alert level changes this year, but daily scans had fallen since.
There was a challenge in getting people to keep scanning when there was perceived to be a lower risk of Covid-19 in the community, the spokesperson said.
"The ministry would like to see an increase in scanning numbers and would like to remind people not to wait for a case to be in the community before scanning in."
The latest update to the app also includes the ability to use a previous scan, save frequently visited locations, and reminders when people haven't scanned or added to the diary in a while.
How many people have been using the app?
Use of the Covid-19 Tracer App has been dropping since March this year, when the country went back to alert level 1 after a community outbreak in Auckland.
QR scanning and manual entries into the app were at their peak in September of last year, just as Auckland moved out of a level 3 lockdown.
At the time, there were five probable and 45 confirmed cases of Covid-19 in the community, and 44 cases confirmed cases in managed isolation and quarantine.
But scans and entries have gone down to less than half of that in July, according to a monthly analysis of Ministry of Health data.
Apart from the first three months of the app's launch, July is not far off the lowest number of app scans and entries. That was in December when it dipped to 16.6 million.
There were neither community cases nor alert level changes that month.
In comparison with March - the last time there was an uptick in use - July had about 17 million fewer scans and entries.