Mixed messaging from Ashley Bloomfield and his deputy on Bluetooth tracing

Positive steps at parliament protest, Covid spreads at children's hospital and tensions remain high in Ukraine in the latest New Zealand Herald headlines. Video/ NZ Herald

Director general of health Ashley Bloomfield says Bluetooth tracing will likely be phased out.

But deputy director general, data and digital Shayne Hunter says it will be kept on. And, defying a trend revealed in an Official Information Act request, he supplied data showing an uptick in Bluetooth alerts as Omicron begins to surge.

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• The Bluetooth tracing shambles - what's happening next

The he-said/he-said saga began on Monday, when Pattrick Smellie - of Herald stablemate BusinessDesk - weighed in during a briefing by Bloomfield and Prime Minister Jacinda Ardern (online here).

Smellie quoted the results of the OIA response, which revealed from February 25, 2021, to January 30, 2022, the Ministry of Health sent just 1317 close contact alerts to devices, based on Bluetooth data - representing just 1 per cent of close contact alerts.

He then asked: "Why is that number so low, and given what you've told us today, how useful now is Bluetooth?"

"It certainly wasn't used very much during the Delta outbreak," Bloomfield responded.

"The expectation is that we will use it into phase 2, until the numbers start to get quite high. It does have some utility because it can let people know, perhaps even faster than they can be contacted through normal contact tracing processes. But we will likely phase it out toward the end of phase 2."

Director general of health Ashley Bloomfield says: "We will likely phase it out toward the end of phase 2." Photo / Mark Mitchell

University of Auckland research fellow Andrew Chen - who had earlier uncovered that most contact tracing staff were too overwhelmed to walk infected people through the process of uploading tracing data from their iPhone or Android to Ministry of Health servers, robbing our Covid response of a vital tool - said he was not surprised by Bloomfield's statement, given the MoH had previously flagged it would phase out Bluetooth tracing in Phase 3.

Deputy director general of health Shayne Hunter said on Tuesday: "We are not expecting to stop using Bluetooth tracing."

But last night, deputy director general Hunter told the Herald, in a statement: "We are not expecting to stop using Bluetooth tracing.

"The ministry will continue to ensure it is used appropriately and is supporting the response. Bluetooth tracing and scanning-in continues to be a meaningful record for people of where they've been. Scanning especially is important as it provides people with their own secure, digital record of their movements.

"The National Investigation and Tracing Centre has and continues to regularly encourage Public Health Units to use Bluetooth functionality throughout this outbreak and confirmed that this is part of standard operating procedures."

(Hunter's statement was labelled a "draft". The Herald asked for clarification but did not receive an immediate response).

Hunter also supplied a spreadsheet that revealed a big uptick in Bluetooth alerts this year.

Since January 1, 3472 Bluetooth alerts have been sent and 972 keys uploaded.

Of those, 2596 alerts and 826 of the key uploads have been since February 1.

How Bluetooth contact tracing works

Where manual QR code poster scanning creates a record of where you've been, automated Bluetooth tracing keeps a log of who you've been in close contact with.

If you've been in close contact with an infected person (and the MoH has played its part, which hasn't happened much as per the main text above), you'll get an alert if you've been in close proximity to an infected person for several minutes. The alerts don't identify the person; they just let you know you were in the danger zone.

Automated tracing and alerts have potential to speed up the alert process as New Zealand moves into DIY care for most who have received a positive test.

NZ's Bluetooth tracing system - which is built into the NZ Covid Tracer app - is based on the Google/Apple Exposure Notification Framework (often referred to as GAEN or ENF).

Image / Getty Creative

In approving Bluetooth tracing in 2020, then Privacy Commissioner John Edwards noted no personal information is shared with Apple or Google. And that your close-contact record is stored on your iPhone or Android in your pocket, rather than in the cloud, as an additional privacy safeguard. The information is only kept on your phone for 14 days. It can be shared with the Ministry of Health if you get diagnosed with Covid, but only if you give your permission.

Once Bluetooth tracing is enabled on your phone, it runs in the background.

Once it's enabled on your phone, you go about your life as usual.

As you wander around, your phone broadcasts an ID number (also known as a "key").

When your phone is physically close to another phone with Bluetooth tracing enabled, for a set amount of time, the two phones exchange keys, and record them in a diary/log.

If one of the two phone owners tests positive for Covid-19, they are then asked by public health officials to (voluntarily) upload the keys on their device to a central Ministry of Health server.

Phones with Bluetooth tracing enabled are checking that server on a regular basis and, if there are new keys, will download them and check them against their log. If there is a match, then the user is notified about the match, and prompted to isolate and get a test.

Importantly, MoH does not know the identity of people who have matched, so this system relies on people doing the right thing when notified.