Covid 19 coronavirus Delta outbreak: Modellers quietly optimistic elimination within reach

Covid-19 modellers are quietly confident New Zealand’s Delta outbreak will soon be stamped out – but say it’s up to all Kiwis to ensure we again reach “elimination day”.

With 20 community cases reported in Auckland today – the lowest count since August 20, in the outbreak’s opening days – Director-General of Health Dr Ashley Bloomfield said New Zealand was “heading in the right direction”.

“But we want to make sure they are the only 20 cases,” he added.

“We can’t let even one case slip through the net.”

Assessing the latest numbers, Covid-19 modeller Professor Michael Plank said he was “cautiously optimistic” about the situation.

“It’s good that we’re seeing a clear downward trend and that the numbers are clearly coming down, and that they haven’t sort of stayed up around that 70 or 80 mark,” said Plank, of Te Pūnaha Matatini and the University of Canterbury.

“I think this shows that elimination is possible. But we have to keep going with what we’re doing. We can’t take our foot off the pedal.”

Plank said, at this stage, it was difficult to tell just how steep the downward trend was – and thus how much longer the outbreak would burn on – although this week’s case numbers would provide more clarity.

In New Zealand’s main wave last year, for instance, the R value – or the average number of other people an infected person passed the virus on to – was squashed down to around 0.4 by level 4.

With Delta, that value could be higher this time around – although we could assume that it had been forced down below one.

Plank said this was contingent on the public following alert level rules, keeping to their bubbles, and getting tested if they developed symptoms.

“Because there’s no guarantees, and things can easily start to go wrong again if the virus catches a chance to spread between bubbles.”

He said that how soon areas outside Auckland could drop alert levels depended on how effectively a boundary could be put in place around the region.

Today, reporters were told that people travelling in and out of the Auckland region for essential work may be soon health-screened at the regional borders.

Health officials were working on advice for tomorrow’s Cabinet meeting, where it would be decided whether the rest of New Zealand, outside of Auckland, could come down from level 3 to level 2 early this week.

“I think it’d be reasonable that some areas of the country could move to level 2 – but you’d have to have a really strong mechanism for stopping people who are potentially infected from moving across the boundary, and between alert levels,” Plank said.

“Once you’re at level 2, it only takes one case to leak out of Auckland, that could cause an explosive outbreak, and we could all be back to square one.”

Fellow Te Pūnaha Matatini modeller Dr Dion O’Neale echoed Plank’s concerns.

“One of the main areas of concern that the modelling highlights as a risk for ongoing spread is spread between dwellings via interactions with essential workers, and any other out-of-bubble interactions,” he said.

“If this happens there is a risk that the outbreak will drag on with a long tail, where there are low case numbers but it takes a long time to reach elimination.”

O’Neale said the new policies and procedures introduced for this outbreak, such as requiring household contacts of identified close contacts to also isolate until a negative test result, was the right approach.

“The new and current test-trace-isolate policies are well designed to minimise the risk of spread for the people who’ve been identified as highest risk in the period before symptoms develop and for asymptomatic cases.”

He said stopping spread in workplaces operating as essential business would also rely on having strong measures in place, both between workers and between workers and customers.

“This means things like wearing masks properly, but also things like rostering staff so that they are working at the same time as the smallest number of other people possible, and that if they are at work other people then they are always interacting with the same set of people,” he said.

“It also means not having workplaces operating if they are not genuinely essential.

“Even with reduced transmission risk, each extra workplace where people are interacting is an addition extra pathway for transmission.”

More generally, though, O’Neale agreed the rapid drop in case numbers over the past couple of days was “very positive”.

“Public health efforts, and the community response, has been very good,” he said.

“If everyone continues to do their part, then it looks like we’re in the right track for elimination again.”

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