Covid 19 coronavirus Delta outbreak: Why an MIQ leak is cause for relief, and how far off is level 3?

A daily wrap of all the main developments in the Covid-19 Delta outbreak as New Zealand is plunged into lockdown for the fifth time. Video / NZ Herald

ANALYSIS:

Never has an MIQ leak been greeted so warmly.

The genomic sequencing results linking the Delta cluster to a recent MIQ case has all but ruled out the spread of undetected cases for several weeks.

Previous modelling - by Professor Shaun Hendy's team - had roughly 100 cases circulating the community at the time the first one was detected.

It was based on the index case arriving two to three weeks ago, with the Devonport tradesman being the fourth link in one transmission chain.

Genomic sequencing has now revealed with 90 per cent probability that the index case flew in from Sydney on August 7.

With the tradesman testing positive on August 17, the most time the Delta variant could have been circulating before detection is 10 days.

Hendy says the estimate of 100 cases hasn't really changed because the benefits of the shorter timeframe are cancelled out by the cluster growing - or expected to grow - faster than previously thought.

But there are almost certainly fewer undetected chains of transmission for public health officials to hunt down, which makes the outbreak easier to contain.

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Health officials are hoping that there is only one chain of transmission.

Currently, there is at least one missing link - how did Delta pass from the Sydney traveller to someone in the cluster?

The Herald understands there have been at least two more confirmed cases since yesterday's update, so the cluster now stands at 22 (excluding the Air NZ cabin crew member, who is not connected to the other cases).

Based on preliminary interviews, all bar two are expected to be linked to the cluster - with interviews continuing.

We should be prepared for more cases, and this morning the Herald understands cases have surfaced in Wellington.

And test results are still yet to come through from most of those who attended the church service, various pubs, or Avondale College.

The size of that downstream tail is still anyone's guess, including whether it has spread outside of Auckland or the Coromandel.

But the strength of the tail has been diminished by the swift move to alert level 4.

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There will be a time for the Government to ask questions about how to improve border defences, including where MIQ protocols fell down, if at all.

But today the focus will continue to be on stamping out Delta, and whether it's safe enough to ease alert level restrictions outside Auckland and the Coromandel from Saturday.

If Jacinda Ardern decides to shift to alert level 3 in the South Island - or in some parts of the North Island - it would be based on a belief that there are no Delta cases there.

She won't be able to know that with any certainty, but she will consider testing results, as well as the number of contacts in different parts of the country.

None of the 362 close contacts identified yesterday are outside of Auckland or the Coromandel, but there are still many unknown close contacts - not only for current cases but cases yet to emerge.

It's unclear if there has been enough testing to give a high degree of confidence that there are no cases in other parts of the country.

Wastewater testing has so far been negative for areas outside Auckland, with Thames and Coromandel results expected today.

Ardern will also be aware that restrictions in level 3 are not enough to keep Delta in check.

As we have seen in NSW, Delta is more likely to infect the whole household if it sneaks into a bubble.

And it's more likely to leap from bubble to bubble at level 3 because bubbles can expand to include close whanau and caregivers.

Events in Australia have recently reminded Ardern of what she has repeatedly said: the last thing she wants is to yo-yo in and out of alert levels.