Why you should keep your contact tracing app

The Prime Minister has announced that QR code scanning, and display of QR codes by businesses, is no longer required. Before that announcement, we were seeing significant decline in QR code scans as we entered the Omicron wave, with manual contact tracing scaled back at Phase 3 of the wave. With locations of interest no longer being published, and therefore no location-based exposure notifications through NZ COVID Tracer, the downwards trend was to be expected.

But there are two reasons to keep the app: for maintaining your own records and Bluetooth tracing.

The fall of QR codes

Our research has identified many factors that influence the decision to participate in digital contact tracing, ranging from availability of smartphones to confidence in technology to privacy concerns. But two of the strongest factors are changes in perception of risk and perception of effectiveness. Throughout the pandemic we have seen QR code scans jump up whenever there were new community cases - a response to the perception of risk suddenly increasing - and then falling slowly over time. The sharper drops more recently can be attributed to decreased perception of effectiveness (plus a general mobility decline as more people work from home).

So, one of the core functions of NZ COVID Tracer - scanning QR codes and generating exposure notifications based on locations - has fallen out of vogue. Does that mean that the entire app is now useless? No, because that’s not the only function of the app.

Scanning QR codes and keeping a track of where you have been is still helpful if you get Covid-19 and need to remember who to notify. It may not be easy to remember who you saw on which days in your infection period. Using this tool is, of course, a personal choice, as there is no longer a central contact tracing apparatus to notify people while keeping your identity anonymous.

It is disappointing that displaying a QR code is no longer mandatory for businesses, as this reduces the ability to collect that information - a major supermarket chain has already ordered stores to remove the codes. Rebuilding infrastructure takes time and if, as the Prime Minister noted, a new variant means we need to scan again, we will not be able to respond as quickly as if we had just left the QR codes up.

The rise of Bluetooth tracing

The use of Bluetooth tracing has become much more significant in the last month. The daily count of over 2.3 million devices participating in the system is equivalent to almost 60 percent of the adult population - one of the highest rates of participation in a Bluetooth-based digital contact tracing tool in the world.

After reporting at the beginning of the Delta outbreak that Bluetooth tracing was not being used at all, contact tracers started using the tool in limited volumes. It wasn’t until human phone calls were replaced with an online self-reporting form, that Bluetooth tracing codes were routinely provided to a higher proportion of cases, leading to a large increase in participation. In the last week, we have seen thousands of cases provide data, and tens of thousands of people issued exposure notifications.

As a reminder of how the system works (skip two paragraphs if you already know this), when you have Bluetooth tracing turned on with NZ COVID Tracer installed, your phone emits randomly generated codes. Other phones listen for these codes and record the ones they hear and how loudly they hear them (based on the “signal strength”). If you later test positive for Covid-19, you are invited to complete a self-reporting contact tracing form for the Ministry of Health, detailing where you have been and when you were symptomatic. Additionally, you are issued codes to enter in the NZ COVID Tracer app voluntarily, which authorises the app to upload your location diary and BT codes to the Ministry of Health.

Other people’s phones periodically check Ministry of Health servers for Bluetooth codes from people who have been infected with Covid and check for matches against the codes they’ve heard, locally on the device. If there is a match, an exposure notification is generated to warn the user, and no information other than an analytics ping (a message to say that a notification has been generated) is sent to the Ministry of Health, maintaining anonymity. Bluetooth tracing doesn’t record where you are, and contacts are matched based on proximity rather than location. While there are scenarios where scanning location-based contact tracing is more helpful, the advantage of Bluetooth is that it runs passively in the background - once you turn it on, it’s running, and users don’t have to do anything else to keep it going.

This system is currently telling thousands of people each day that they may have had contact with someone who has Covid. It means those people are better informed to evaluate day-to-day risk. Maybe I should work from home and move a few meetings online. Maybe it’s safer for me to not go to that birthday party tonight. Maybe that sore throat is more than just talking too much and I should do a RAT. The exposure notification indicates a person may have been exposed to Covid, rather than evaluating risk based on the general vibe.

Of course, the system is not perfect. Less than 10 percent of daily cases are voluntarily uploading their Bluetooth tracing data, although this may increase as the Ministry of Health has adjusted the self-reporting form to provide the NZ COVID Tracer upload codes earlier in the process. There will be plenty of people out there who have been exposed but are missed by the system entirely. Bluetooth signals are significantly impacted by the environment which reduces the accuracy of the system. The system doesn’t know if you were wearing a mask or were in a well-ventilated area when you were near an infected person, so there will be false positives. The system also still operates on contact thresholds better suited for the Delta variant rather than the even more infectious Omicron. These are all weaknesses in this system that we should acknowledge.

Keep the app

But in a landscape where we are increasingly taking care of our own safety and mitigating our own risks, many of us want more information rather than less to improve our decision making. The Bluetooth system is contributing some value, which is probably better than nothing. Fears of the “pingdemic” as seen overseas haven’t eventuated here, which could cause us to ask why this tool wasn’t used more widely, earlier. Maybe if we had used it more in previous phases, there would be more awareness and confidence around the tool now.

The upshot of all this is that, if you have Bluetooth tracing enabled with NZ COVID Tracer installed on your phone, don’t uninstall the app just because you aren’t scanning QR codes anymore. If you delete the app, the system will no longer work and you won’t receive notifications. Of course, participation in Bluetooth tracing is voluntary, but its effectiveness relies on a high proportion of the population using it. And if you get sick with Covid and are asked to fill out the contact tracing form, do consider getting the NZ COVID Tracer upload codes and providing your Bluetooth tracing data - it’s one of the last ways of reducing the spread of the virus and helping keep the people around you safe.