The Government's removal of mandatory QR code scanning has seen Covid Tracer app usage for that purpose plummet — but not Bluetooth tracing.
Ministry of Health data released on Thursday night shows the number of people receiving notifications because of the app's Bluetooth function after being exposed to someone with Covid-19 has remained steady in the past month.
Researcher Dr Andrew Chen, from the think tank Koi Tū: Centre for Informed Futures at Auckland University, told 1News while Bluetooth had its limitations for contact tracing, people who did get pinged should take it seriously.
"Now that scanning is not mandatory and locations of interest aren't being published, [Bluetooth tracing] is one of the only tools we have left to provide people with information so they can make a risk assessment and make their own decisions."
Chen argued that was why people who used Bluetooth tracing should keep their Covid Tracer app installed even if they didn't use it to scan QR codes. Without the app, the device wouldn't be able to receive Bluetooth notifications.
The Bluetooth tracing system, when activated, works by getting devices to emit randomised signals to other devices nearby. In turn, other devices record which signals, or 'keys', they detect.
If someone tests positive for Covid-19, they can be given instructions about how to upload their keys to a server if they choose to. Those keys are then pushed out to devices using the Bluetooth tracing system where they are compared to see if there's a match.
Whether or not someone receives a notification of Covid-19 exposure after a match depends if they reach a certain threshold. That threshold is represented by a score calculated using an algorithm that considers the strength and duration of Bluetooth signals between two devices as an estimate of the time people spent together and their proximity to each other.
Currently, that roughly equates to being two metres away from someone with Covid-19 for about 15 minutes.
The increase in the number of devices uploading and receiving Bluetooth keys for contact tracing had happened relatively recently. In August last year during the Delta outbreak, while health officials demanded speedier contact tracing and focused on finding locations of interest under an elimination strategy, the technology was hardly used.
Chen attributed part of the recent increase in Bluetooth tracing use to the increasingly automated way a majority of Covid-19 cases were being handled.
Early in the pandemic, a contact tracer could decide whether a person's QR scanning data was enough or they needed a person's Bluetooth information too. Now, an online self-reporting system meant more cases were provided with a code to be able to upload their Bluetooth data to the server.
Still, fewer than 10% of reported daily cases were opting to upload their Bluetooth data. Their contacts also needed to have Bluetooth turned on. On top of that, there were inherent reliability issues with the technology.
"So, lots of potential contacts are being missed," Chen said.
The app's developers had also recently tweaked the threshold at which a person would receive a Bluetooth notification in line with the Government lowering isolation times. So, after being in contact with a person with Covid-19, their phone would only alert them if they'd seen the person in the past 10 days, rather than 14.
But Chen believed the way the app was coded was still more aligned with Delta, rather than the more-transmissible Omicron. It also didn't consider a person's vaccination status, mask use, or whether they were indoors or outdoors when they'd come into contact with the virus.
"So, there'll be lots of people who are missed [through Bluetooth-based exposure notifications]. So, if you are getting one, you should take it pretty seriously."
Director-General of Health Dr Ashley Bloomfield said the Covid Tracer app's Bluetooth function was "one good reason to keep it on your phone".
He added that while the requirement to scan QR codes had been removed, "it may still have value for us".
"This virus has thrown curveballs our way to date and there may well be another one coming our way. In which case, the app and therefore the ability to scan could play an important role."