The Ministry of Health has resumed using Bluetooth tracing functionality built into its Covid-19 Tracer app, after a two-week pause amid the Delta outbreak.
The Bluetooth tracing system, developed by Apple and Google, transmits a signal from one phone to nearby phones when turned on. That allows phones to swap "randomised keys".
If someone tests positive for Covid-19, they can be given instructions about how to upload their keys to a server. Once uploaded, those are then downloaded to devices using the Bluetooth tracing system where they are compared with other users' keys to see if there's a match.
For the first time since August 17, the start of Alert Level 4 restrictions, the Ministry of Health sent keys to people’s devices — once on Tuesday night and again on Wednesday afternoon — with data going back to August 18.
AUT computer science professor Dave Parry, on sabbatical at Perth’s Murdoch University, said a likely reason why Bluetooth was being used again was because of a change in workload for contact tracing teams and the current state of the outbreak.
“With everyone locked down so much, the number of ‘false positives’ generated by the Bluetooth system will be much lower – people simply aren’t mixing so much,” Parry said.
He said there was also a possibility that data from scanning QR codes could be “less informative” as lockdown continued. For example, that meant people weren’t going to big venues, but could potentially be near others.
So, this meant potential exposures which could be identified through Bluetooth were becoming more important, Parry said.
“I expect there is a bit of experimentation going on to see how useful this is so that, as we come out of lockdown, the tracing teams can use this effectively.”
Andrew Chen, a research fellow from the thinktank Koi Tū: Centre for Informed Futures at Auckland University, said he was “glad” to see the Bluetooth tracing system being used again.
“But, I'd still like to know why exactly it wasn't used earlier in the outbreak so that we can understand and learn how to respond to future outbreaks better.
“Given that everybody's been asked to participate in the system, and people have felt that this tool gives them some protection, we should know why it hasn't been used.”
Data released to 1 NEWS as of Saturday showed “[fewer] than 10” notifications were sent to people’s phones as a result of Bluetooth tracing on the Covid-19 Tracer app in the Delta outbreak.
A Ministry of Health spokesperson told 1 NEWS at the time this was for a number of reasons. These included “inherent reliability issues” with Bluetooth technology to be able to assess risk of transmission, the lack of people in the outbreak using the technology, and the volume of data that needed to be sifted through while the virus was still spreading.
The spokesperson said traditional contact tracing techniques were being used, and that Bluetooth was meant to support and not replace those methods.
"As the outbreak changes, and more emphasis goes on to fewer locations, the Ministry will be working with public health units to assess whether Bluetooth activation with positive cases in the small number of workplaces (seven to date) may assist,” the spokesperson said in a further statement on Monday.
Some people questioned those reasons, including ACT leader David Seymour and National Covid-19 response spokesperson Chris Bishop.
Speaking in the House on Tuesday, Covid-19 Response Minister Chris Hipkins said contact tracers used the “best information that is available to them”, and that Bluetooth was only one of those.
“They will make judgments about whether the data that they’re getting out of Bluetooth, or out of the QR code scanning, or out of the other methods is the best data to use in the context of a specific case investigation,” Hipkins said.
Chen also questioned the reasons the Ministry of Health gave for not using Bluetooth tracing earlier.
“They kind of pointed to both ‘false positives’ and ‘false negatives’ as a reason to not use it. Not that they use those terms, but that's what I translated it to. And that seems to tell me that they don't really know why either.”
He said the country’s current approach of classifying more people as contacts, in a response to the highly-contagious Delta variant of Covid-19, also produced a lot of false positives anyway.
“A second part is that I very much appreciate and understand that the contract tracers are at capacity, and that they are doing their best to chase down all of the possible contacts. So, if there was a decision that Bluetooth should be de-prioritised and it was for a particular reason, that could be legitimate,” Chen said.
“I don't think I'm satisfied yet that that is what actually happened.”
That’s because part of what Bluetooth was meant to do was “automate some of that process of finding contacts”, he said.
“I don't think you can rely on the demographics argument either. … That is trying to put the emphasis back on those cases for their failure to have used the app and to not have Bluetooth tracing on, rather than what appears to have been a public health decision to systematically not use that Bluetooth data.”
Parry, on the other hand, echoed some of the reasons the Ministry of Health offered.
“It seems to me that the public health tracers aren't finding [Bluetooth] useful, that they don't really think that it adds much to their ability to trace contacts … and one of the big things, of course, is doing it quickly to reduce an outbreak,” he said.
“Bluetooth detection really works by saying that the devices are probably within a few metres of each other. They can't really tell — they have to tell by the strength of the signal for a certain amount of time.
“That may or may not be an accurate description of how the virus transmits.”
1 NEWS has contacted the Ministry of Health for comment.
On Friday, Deputy Prime Minister Grant Robertson said the decision to re-start Bluetooth tracing, despite the reliability issues that the Ministry of Health had pointed to, was made because it was "another tool in the toolkit".
"We continue to want people to scan, even in higher alert levels where there are limited places that you can go. Bluetooth provides another additional piece of information for us," he said.
"That's why it's been put back in place."
Director of Public Health Dr Caroline McElnay said Bluetooth tracing was another method that could be used to help identify contacts of cases.
What is the future of Bluetooth tracing in New Zealand?
Chen said not having used Bluetooth tracing earlier was a missed opportunity for New Zealand to test whether or not the technology was useful in a country that had eliminated Covid-19 prior to the latest outbreak.
He said New Zealand wasn’t “quite at that point yet” to conclude Bluetooth wasn’t useful and that it shouldn’t be used at all.
“There's a theoretical evidence base from the modelling. There is also some evidence that we can look to overseas but the contexts are also still quite different to ours.”
If Bluetooth continued to be used in New Zealand for any future outbreaks, Chen said the Ministry of Health would need to consider changing their processes.
He said, for example, people could be emailed instructions about how they could upload their Bluetooth keys into the server instead of a contact tracer having to give them the codes and having to walk them through how to do it.
The settings that determine whether or not a person receives a Bluetooth alert should also be tweaked to take into account Delta’s more transmissible nature, Chen said.
Currently, the NZ Covid Tracer app’s Bluetooth function is coded to calculate a score that assesses the risk someone has contracted Covid-19.
A score is calculated based on the strength and duration of Bluetooth signals between two devices, which acts as an estimate of the time people spent together and their proximity to each other. It also considers how infectious a case would have been on that day.
Only a person who passes a certain score threshold would receive an alert. Currently, that approximately equates to two people together, two metres apart, for about 15 minutes.
“I don't think we want to get to a position where people lose confidence or lose trust in the app because it feels like everybody's being told that they're close contact. And, certainly with Bluetooth, there are significant concerns about the reliability and accuracy of technology because the error rates can be quite high,” Chen said.
“So, we just need to be careful with what we reduce the thresholds to. They should be lower but not too low.”
The introduction of mandatory record keeping in some locations would also make a difference to contact tracing efforts, he said.
Parry said artificial intelligence could enhance current methods of calculating those scores, for example, by considering how infectious a person was and whether a person is inside, in a ventilated area, or outside.
“These things can get quite complicated, but we can get the raw data and play with that,” he said.
Parry said Bluetooth tracing could also be useful in summer, when people spend less time indoors, and among young people who tend to interact with more people in different places.
He also suggested a public education campaign about how Bluetooth worked.
“So, you want the public to know, ‘OK, if I get [an alert] from Bluetooth, this doesn’t mean I definitely got Covid, but it doesn’t mean I definitely haven’t either and I’ve got to do something to check.’”
Alternatively, Bluetooth could be used to help researchers study how people moved around large environments like schools so changes could be made to help people stay safe, he said.
“We could get a model of how much exposure they’re getting … to understand where transmission might occur,” Parry said.
“You could say it’s a really good outcome that we haven’t had to use [Bluetooth tracing] because if we can do tracking and tracing without having to use Bluetooth data — it’s probably more reliable and there’s more chance of getting it right if we know exactly where people were and what they were doing.
“Against that, we are going to be living with [Covid-19] and it's worth putting some effort in and following what people are doing around the world in order to get this [technology] as effective as possible.”