That puts other concerns in perspective.
Despite doubts or frustrations people might feel over the vaccine rollout or the Government's overall strategy, sticking to the elimination plan and overcoming this dangerous hurdle has to be the focus for now.
People in Auckland and Coromandel at least should be prepared for a long wait as the emerging cases point to a large cluster.
Genomic detective work has book-ended the start of the sequence to a traveller from New South Wales on a red zone flight two weeks ago.
That provides a helpful timeframe with the coronavirus loose in the community for a shorter period than initially feared. Professor Shaun Hendy said: "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."
Severely limiting people's movement, the use of masking, testing and tracing will hopefully prevent further spread. But the amount of known exposure is unsettling. The hunt for the other book-end continues.
The wide geographical spread of cluster cases has been one of the alarming aspects of this Delta outbreak.
In previous short shocks, people could look at lists of "locations of interest" and immediately feel somewhat reassured, from a personal viewpoint, if cases were centred on suburbs or towns kilometres away.
This time, the list of more than 100 exposed sites includes spots in the CBD; Grey Lynn, Avondale, New Lynn further west; Northcote, Birkenhead, Takapuna and Albany to the north; East Tamaki and Remuera out east and Papatoetoe and Mt Wellington heading south.
And so many are normally busy places suited to easy virus-hopping such as shopping centres, stores, supermarkets, bars, cafes, a university, school, cinemas, service stations, fast-food outlets, Sky City casino, a church, and buses. The trails of normal life - picking up groceries, catching a quick bite, filling up the car, a night out - now being mapped by Covid tracers.
That's a lot of potentially infected people to track down in order to find the outer edge of this cluster. Delta's extra transmissibility gives contact tracers less time and one of its characteristics is it spreads among the young.
Professor Michael Plank said: "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."
The Government and health authorities will be encouraged by how people have generally responded - coming forward for tests, staying home, wearing masks and booking vaccinations.
Prime Minister Jacinda Ardern said that the first day of lockdown saw 195,537 bookings - the highest ever. The Delta blues may have encouraged some waverers or less concerned types that they should get it done.
On the Coromandel, where there are at least a dozen cluster sites of interest, people lining up to be tested at a pop-up centre were being encouraged to visit a vaccine centre nearby. Which is a smart approach.
The PM gave vaccination momentum a nudge by announcing that the Pfizer/BioNTech jab would be available to 12-15-year-olds, which would help boost the country's overall collective immunity.
Ultimately, stamping out this Delta outbreak is about returning to safety but also about once again buying time for people to get vaccinated.
