Coronavirus: Will Aucklanders seed a Christmas explosion of Delta across the country? Experts make predictions

With a bit of luck, Auckland might be able to pull off a New South Wales and reopen without experiencing uncontrolled spread of Delta, experts say. 

But the timing of it - right before Christmas - could expose less-vaccinated parts of the country over the holiday break, seeding potential outbreaks that could explode when school resumes in February.

New Zealand's seven-day average has stabilised at just under 200 cases a day - mostly in Auckland, while New South Wales has pulled its down from 1400 in mid-September to just over 200 now - despite celebrating a 'Freedom Day' in early October. 

"There were these predictions that there would be a really rapid uptick in cases - instead what we've seen is a modest increase in cases that has basically levelled off," Chris Billington, a disease modelling expert at the University of Melbourne, told The Project. 

And something similar has happened here, at least for now. While cases rose rapidly after the shift from level 4 to 3, in the past week that growth has stalled. Dr Billington's calculations suggest the R number in New Zealand - the number of people each infected case will pass the virus onto - is at about 1.03, possibly below 1 already, meaning the outbreak has indeed stabilised or could be starting to wane.

Assuming we keep getting vaccinated at the current rate, his modelling shows the outbreak will fade away - dropping to 25 cases a day by March. But that assumes we won't be relaxing restrictions, which we will be on December 3 when the alert level system is dropped for the 'traffic light' COVID-19 Protection Framework.

Chris Billington.
Chris Billington's analysis of how the outbreak might go with vaccines, but keeping level 3 in place. Photo credit: Chris Billington

School is also likely to be back fully by then too, and in the meantime there's Christmas festivities to worry about. From December 15, Aucklanders will be allowed to leave the city - adults will need proof of vaccination or a negative test, while children won't. 

"It will probably mean that we have cases scattered across most of the country over the summer period," University of Canterbury modeller Michael Plank told The Project, noting that one-in-five cases in the current outbreak are under 12, so exempt from the vaccinations and testing requirements. 

 If that's the case, then back to school in February will be a real crunch time." 

Medsafe is yet to approve the vaccine we're using, made by Pfizer and BioNTech, for kids under 12. The US is already rolling it out for kids as young as five, and Canada will soon join them. Pfizer's trial showed the vaccine is "safe, well tolerated and showed robust neutralizing antibody responses", and it's now investigating its efficacy and safety in children under five. 

Booster shots for people aged 12 and over will start next week. People will be eligible six months after their second dose, around which time the vaccine's efficacy appears to wane. 

Tony Blakely, a University of Otago epidemiologist based in Melbourne, told The Project booster shots for adults is "mission critical" if we're going to hold off a post-summer surge, but getting children vaccinated will be just as important. 

"If we vaccinate them in January and February say, before we all start getting our boosters, that might help bridge us across without too much infection happening." 

Dr Blakely contradicted most other experts a few months back when he predicted opening up wouldn't see an explosion in cases in NSW

"They turned it on its head by really high, fast vaccination into those [local government areas] of concern… then high vaccination coverage across the state. And... they've been lucky since then. 

"They've shouldered about 200 cases per day - I would expect that will start going up soon. The reason it's down there now is so many people have been recently vaccinated and the vaccine immunity hasn't waned. But that waning will start to creep in, then we'll start doing Christmas stuff and it will probably go up a little bit over the Christmas period."

Dr Plank said NSW's introduction of vaccine passes has also helped.

"New South Wales has been using vaccine passports and they have been effective there in controlling transmission and bringing rates down. That bodes well for our move to the traffic light system."

Dr Blakely isn't sure if New Zealand will be as lucky as NSW, purely because of the timing - opening up just ahead of Christmas. But if cases do start to spiral, at least it's happening after most of us got vaccinated. 

"You have now got nice decoupling - the number of people going to hospital, the number of people in ICU in New Zealand is really quite low at the moment because of that vaccine effect."

More than two-thirds of all New Zealand cases of COVID-19 have come since August 16, but only one-third of our related deaths. While Delta is better at infecting vaccinated people than earlier strains of the virus, vaccinated people are far less likely to require hospitalisation or die. 

It's hard to see 'decoupling' in New Zealand's data because both our case and death numbers have been low, but it's easy to spot in the UK. They're recording about as many cases every day now as they were in the surge over the Christmas/New Year period last year, but only recording a small fraction of the deaths. 

After a late start, New Zealand is now one of the most highly vaccinated countries in the world - 27th by whole population, according to the New York Times

"Thanks to the vaccine, it's possible a lot of cases will fizzle out before they have a chance to get established in the local community," Dr Plank said in separate comments on Tuesday.

"With schools out and workplaces quiet, total case numbers may remain relatively stable over the summer period. However, communities with low vaccination rates will be vulnerable to rapid outbreaks that could overwhelm health services in remote rural areas. 

"Once schools and workplaces go back in the new year, the virus will be able to spread more easily and there is a danger that case numbers could take off with multiple outbreaks across the country."