The visiting family at the centre of our first major Omicron outbreak may have encountered a hidden chain of transmission that had been silently building in Auckland for days.
Experts have also told the Herald that, with no epidemiological link so far, it's unclear how the incursion occurred - and we may never know.
Officials now face the daunting task of tracking down hundreds to thousands of potential contacts - so far spread across a wedding, theme park, shopping mall, bus trips and flights, and two main centres – all in the face of a fast-moving variant capable of doubling infection numbers every three days.
Here's what we've learned so far.
On Thursday, January 13, nine members of a Motueka family flew to Auckland for a wedding, which they attended for four hours that Saturday at New Lynn's Totara Event Centre.
The venue's manager told the Herald there were around 80 people at the wedding, all of whom were vaccinated and abided by Covid-19 restrictions.
Yesterday, two other cases were added to the cluster: an Air New Zealand staffer who was on the Sunday evening flight back to Nelson with the family, and a South Auckland rest-home worker who was also connected to the family.
Another eight were confirmed today: two in the Nelson-Tasman region who are contacts of the cases, and five in Auckland linked with one of the events the family attended.
Other busy locations linked to the cluster included Rainbows End (where a case visited between 1pm and 3.30pm on January 16); the Archie Brothers Cirque Electriq arcade in Westfield Newmarket (from 7pm to 9.30pm on January 15); and Flat Bush's Summerset by the Park retirement village, which employed a kitchen worker that had had attended the wedding.
Once back in Motueka, members of the group visited a supermarket and a medical clinic.
The infected flight attendant, meanwhile, went on to work aboard flights between Auckland, Nelson and New Plymouth in five instances.
On top of that, places linked to potentially-infected close contacts included Mission Bay's Tarka Indian Eatery (from 4pm to 5pm on January 14); SkyTower Auckland (from 10am to 11am on January 16) and several bus trips around the city.
"But, even more importantly, we don't yet have a clear lead on the index case that links this family to the border, as we have with our other Omicron cases to date," Prime Minister Jacinda Ardern told media on Sunday.
"That means Omicron is now circulating in Auckland and possibly the Nelson Marlborough region, if not elsewhere."
This cluster was unlinked to Omicron cases in Palmertson North.
Public health experts had long been warning that a steady build-up of Omicron cases at the border would ultimately end in an outbreak – be it through an infected traveller, an airport, sea port or MIQ worker, or an airline crew member.
Otago University epidemiologist Professor Michael Baker argued this episode might have even been delayed had the Government taken steps he and his colleagues had been pushing for, such as limiting flights into the country.
As at this afternoon, the source of the outbreak was unclear - but it appeared likely that the unfortunate family had encountered Omicron during their weekend in Auckland.
"These Auckland cases are all linked, either directly or through secondary contacts, to the family event and other events on the weekend of 15 and 16 January in Auckland," a Ministry of Health spokesperson told the Herald.
Otago University epidemiologist Dr Jemma Geoghegan said it was possible Omicron could have taken an "alternative route" in the community.
"We've seen a fair few air crew members test positive over the last couple of weeks – so that's potentially a likely source."
Professor Nick Wilson, an epidemiologist at Otago University, agreed.
"It could have been someone in MIQ who was missed, but that's fairly unlikely: which leaves someone like an airline worker, or even someone in a shipping crew that's been flown in."
One of the family events, perhaps the wedding, thus could have connected a hidden chain of transmission with the now-identified cluster.
"It could be a missing link, or several missing links, that we haven't found, or may not find," Geoghegan said.
With its short incubation and generation time, Omicron had been shown overseas to spread at such a rate that people could become infected and pass it on before they developed symptoms, let alone seek a test.
"It's definitely possible that there could have been a number of generation times since the index case, given such a large proportion of Omicron cases are either asymptomatic or have mild illness," Wilson said.
Earlier modelling by his colleagues had shown that, even before Omicron emerged, an outbreak that largely spread among children could go undetected for several weeks.
Geoghegan said the fact there was no epidemiological link to the border also indicated that more than one chain of transmission was involved.
"That's kind of what's happened in previous outbreaks: those ones that have resulted in numerous cases in the community have often been ones with no known link to the border," she said.
"They're usually the ones that have been simmering for maybe a week before we even pick them up. So, it's not surprising that's happened again."
Today, the ministry said it expected the number of cases and contacts to grow, given the nature of Omicron and what tracers learned from case interviews.
At the moment, New Zealand's trace-test-isolate system could trace around 1000 cases each day, and manage about 11,000 initial contacts, by working both forward and backward.
"The speed that Omicron spreads at makes it more difficult for contact tracers, but the advantage we have at the moment is that we're dealing with relatively small numbers," Covid-19 modeller Professor Michael Plank said.
It was difficult to say when – or if – the outbreak might grow to the point it reached thousands of daily cases, forcing the Government to reclassify contacts as part of the third stage of its new playbook.
"Right now, we're in a containment phase where we're really trying to delay Omicron getting a firm grip and going into exponential growth."
However, like Geoghegan, Plank pointed to the likelihood that an entire chain of transmission hadn't been found - "and of course, there could be significant onward transmission from cases we don't know about yet".
In light of this threat, he expected that pinning down the incursion's source wouldn't be such a priority now.
"It's always interesting to look at these things ... but it's probably less important now than it was in the past."
While there was still the possibility this outbreak could be bottled up, Baker wasn't so optimistic.
"Usually when we have outbreaks, we do two things: one is controlling it, and two is finding the source to stop it happening again," he said.
"Unfortunately with Omicron, neither of those things are so important now, because, based on international experience, it's accepted that we can't actually stop it spreading."
Whether we could still boost enough of the population, and vaccinate enough children, to greatly off-set Omicron's force remained to be seen.
"But I think it's just the sheer spread of these outbreaks overseas that makes it very daunting: and we can almost exclude the idea that we'll effectively suppress it for very long."