Covid 19 Delta outbreak: why the government is rethinking contact tracing


New Zealand today marked a major milestone in vaccination, with 90 percent of eligible Kiwis having now received at least one dose of the Pfizer vaccine. Video / NZ Herald

Digital tools like the NZ Covid Tracer app are set to become even more important to New Zealand’s pandemic response, experts say, as officials change their contact tracing strategy to deal with the significant number of cases.

Whether contact tracing can keep up with the growing number of daily cases has been a critical question surrounding the Delta outbreak, with 185 more infections added to the tally today.

The Ministry of Health has now restricted its approach to focus on “very close” and “close” contacts of people infected with Covid-19, rather than on “occasional” or “occasional more” contacts, such as people who were briefly in the same place at the same time.

“This was prompted by our analysis of the secondary attack rate, which showed that more casual contact did not result in any positive cases,” a department spokesperson told the Herald in a statement.

With this change, the system was “facing” the current moving average of 154 new cases each day.

The ministry was now in the process of setting up a national case investigation service, which is expected to increase capacity to an additional 150 cases each day, while allowing it to be established over time.

While the system in which public health units operated was designed to handle between 180 and 270 cases per day during the national lockdown, tracing efforts during the Auckland Delta outbreak did not reach those totals.

The ministry acknowledged that “the very high levels of complexity” seen in business in October had “impacted estimates” of what could be achieved under a system that also tracks casual contact.

“Taking this approach, at the time, meant that it was estimated that public health units had the capacity to handle between 100 and 120 cases per day, with the ability to scale up to 150 cases per day for periods of time. limited periods. “

With the number of cases on a growing trajectory – health experts warned this week that the daily tally could reach 1,000 by Christmas if the spread intensifies further – Professor Shaun Hendy, modeler of Covid-19, said a change in approach was needed.

The new dynamic was illustrated by the fact that places of interest were no longer widely shared, while far fewer cases disclosed each day were epidemiologically linked.

“The contingency plans we had in place were based on scenarios like in August of last year, where we could still eliminate, and we could build surge capacity to handle a large number of cases during a short time, ”Hendy said. , by Te Pūnaha Matatini.

“As we now enter a different phase, where we obviously have a tolerance for cases – particularly in Auckland – so what you need is a much more sustainable contact tracing approach. “

He expected that while contact tracers would still spend a lot of time reaching people in vulnerable parts of the community, our response would increasingly rely on electronic tools.

“Now that the outbreak is much more widespread in Auckland – and we’re going to move to a traffic light system where we’ll tolerate cases across the country – we really need scalable solutions. “

This meant a diet that didn’t require as much direct interaction with contact tracers, but relied more on people’s ability to self-manage and self-isolate, he said.

Even so, he said contact tracing would continue to be essential, “because we know that vaccination alone is not enough to control the delta.”

“So I think it’s really important that we put in place a sustainable contact tracing system, which can operate at a reasonably high capacity for several months, if not years.”

University of Auckland tech expert Dr Andrew Chen agreed that more automation through tools like the tracking app could help increase workload capacity.

While people’s use of the app has been poor over time, he said recent data was more encouraging, especially in Auckland.

“At Level 3, Stage 2, for example, we see a 12% increase in QR code scans each day compared to the same day last week, which I guess reflects the increased mobility around Auckland,” did he declare.

“We are now seeing numbers in the order of 2.7 million daily QR code scans. I would expect that, once everything is open and everyone is out like in level 1 conditions, we could see four to five million QR scans per day. “

As for the other key part of the app, around 2.26 million people had Bluetooth tracking enabled, which is roughly 60% of the adult population.

“This means that we have a very high proportion of people using it compared to other jurisdictions – places like Europe, for example, are very happy to have 20-25% of the population using tools. for Bluetooth contact search.

“Because we’re at 60%, we should definitely be thinking about how we can use it to support the contact tracing processes. “


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