• There are a total of 21 Delta Covid cases, an increase of 11
• The NZ outbreak has now been linked to a traveller from Sydney
• Two infected people are now in hospital in a stable condition
• Police confirm arrests for lockdown flouters
New Zealand's Delta outbreak may now be "more contained" than first feared, a virologist says, after overnight genome sequencing secured a critical piece of the puzzle.
But experts still warn that the scale of the outbreak, which has so far grown to 20 cases, could still number around 100 infections.
Today, it was revealed Auckland's community positive cases were a close genomic match with a recent returnee from Sydney on a managed red zone flight on August 7.
That person returned a positive result on August 9 and was transferred from Crowne Plaza to Jet Park on that same day.
As officials could now work on the assumption the current cases came from the traveller, a search for the missing links in the infection chain was under way.
"There's a genomic match to a case in MIQ, which strongly suggests this may be - or at least close to being - an index case of this cluster," ESR and Otago University virologist Dr Jemma Geoghegan said.
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"We now know when they arrived in the country, which wasn't too long ago, which means that we know the likely timeframe that it may be have been in the community.
"And this all means that it's likely that we're dealing with more of a contained outbreak than we initially had thought."
There are now 21 Delta Covid cases in Auckland, including two in hospital.
Nineteen are in the Auckland quarantine facility.
Twelve of the 21 have been confirmed as part of the same Auckland cluster. A further eight are being investigated and are expected to be part of the cluster.
The other - an air crew member - is not expected to be linked because it is a border-related case.
Two people were taken to North Shore Hospital overnight. One had worsening symptoms and the other had underlying conditions. One is in their 20s and one in their 40s. Both are stable.
Geoghegan said the matching genomic results could only link the cases - but couldn't tell tell how the virus had spread.
"What we need to do now is overlay that crucial contact tracing and epidemiological data to help inform that transmission chain, and the direction of transmission."
Te Pūnaha Matatini Covid-19 modeller Professor Shaun Hendy agreed the discovery of a possible link to the border was good news.
"If it holds up under further investigation then the later arrival date means that we are looking at a much shorter chain of transmission and fewer cases than the early results suggested."
He said previous estimates around the size of the outbreak did change if we assumed the virus arrived in the community around August 8 or 9.
"But," he added, "the late introduction also means that we saw a very large amount of spread mid to last week - these two factors roughly cancel out.
"So the good news is that the likelihood of undetected chains of transmission is lower, but our estimates of spread by Wednesday, given the cases we now know about, is still around 100."
Fellow Covid-19 modeller Professor Michael Plank said the fact that the person arrived from Sydney on August 7 meant the virus probably wasn't in the community for more than 10 days before it was detected.
"So that's probably the sort of least worst scenario we could have could have hoped for a moment."
But Plank said location was also a factor.
"We've just learned there's been about 2000 close contacts across the SkyCity Casino, so there's still the potential that we could have had a number of big super-spreading events," Plank said.
"And that's going to be the next big thing to look out for as the results of testing those close contacts come in."
Plank said alert level 4 will have stopped the virus for now.
"Although we're seeing huge numbers of contacts at the moment, going forward, we should see less of that."
Some of the big questions, he added, were how many close contacts would test positive, which would help determine how serious the outbreak was, and just how the lockdown would affect transmission.
"We've seen in Sydney that if it gets into essential workers, it can be really difficult to stop it from spreading," he said.
"The fact that we've acted quickly here and gone into a strict lockdown will definitely act in our favour.
"But we'll just have to wait and see - particularly when it comes to the second part of next week - to see what effect lockdown starts to have on case numbers."