New Zealand is in a good position to make it through summer without a massive outbreak of COVID-19, but it's not looking quite as unstoppable as last year's, experts say.
As 2020 drew to a close, there wasn't a trace of the virus in the country. But half a world away a new, highly contagious form of COVID-19 was starting to spread. After ripping through India, the Delta variant quickly became the dominant strain worldwide.
It broke through our defences in August, and as soon as October the Government had all but abandoned the world-renowned elimination strategy, meaning Kiwis now face their first summer of living 'with' the virus in our midst.
Already the uncertainty has seen a number of events pull the plug, including Auckland's Armageddon Expo, Masterton's Golden Shears, the Wanaka rodeo and numerous New Year celebrations. Others, like Rhythm and Vines and My Chemical Romance's Auckland show, have been postponed.
But is the caution justified? Or is Siouxsie Wiles' 'staycation' the name of the game this summer?
The daily case numbers in the present outbreak rose rapidly after Auckland moved from level 4 restrictions to level 3 in late September. While some queried whether the move was premature, considering previous success New Zealand had in using lockdowns to snuff out outbreaks, the Government said level 4 restrictions couldn't be justified because the virus was largely circulating amongst communities who weren't following the rules anyway, and within households, unaffected by restrictions on movement.
Daily numbers rose rapidly, reaching more than 200 in mid-November, before a similarly steep decline that continued through the first week of December. The country moved into the 'traffic light' system on December 3, lifting most restrictions on movement for those with vaccine passes.
By December 8/9, analysis by University of Melbourne disease modelling expert Chris Billington suggested the outbreak's R number was about 0.8 - meaning each case is infecting fewer than one person on average, a trend that left interrupted would lead to the virus' eventual elimination.
Dr Billington's calculations are based on prior case numbers and the effect of vaccines, and suggest the outbreak could fizzle out by late February or March, thanks to our impressive vaccination rate. But he said it was too early to say what effect the shift to the traffic light system would have, as it wasn't something baked into his model.
"Naively though, we might expect New Zealand to have a similar experience to NSW and Victoria in Australia - which is that the case numbers will level-off and remain roughly flat at whatever level they are at [about] two weeks or so after the easing of restrictions," he told Newshub.
"On the current trend, we might expect that to be somewhere in the vicinity of 50 and 75 cases per day for New Zealand. But there may be pockets of lower vaccination that could result in slow growth still.
"And if a chain of transmission of the Omicron variant were to become established in New Zealand, at the rate it's likely to spread, it would dominate the total caseload and result in overall rapid growth about three weeks after the first case."
Because the virus can incubate for up to two weeks, it usually takes a week or two for the effects of a major policy change to show up in the daily numbers.
'High transmission scenario'
Modellers at Te Pūnaha Matatini, whose work has helped inform Cabinet's decision-making, also said it was too early to tell what effect the traffic light system would have. Michael Plank (also of the University of Canterbury) told Newshub we had been tracking "reasonably closely to what we called the 'high transmission scenario'" the group outlined in October, but "cases have fallen a bit more sharply than we projected" since the mid-November peak.
"We're going into the new traffic light system in a reasonably favourable position: cases have been declining in recent days and hospital and ICU numbers have remained relatively low. COVID has been introduced in small numbers to several different parts of the country but so far hasn’t sparked a big outbreak, even in areas that were at level 2."
Te Pūnaha Matatini's models use complex algorithms taking into account data around movement, household sizes, infectivity, demographics and more. Like Dr Billington's model, it shows the current R number is below one - but it "wouldn’t take much of an increase in contact rates to push it back above one".
"If and when that happens, they’re likely to increase exponentially week on week until something changes to bring them back down," said Dr Plank.
"That 'something' could be wide uptake of boosters, it could be vaccinations of five-11s, it could be accumulation of infection-acquired immunity (though that would likely take a lot of cases) or it could be behavioural change."
Gaps in the defence
So what specifically could cause a large outbreak that ruins our summer?
Whatever it is, it's likely it'll be able to be traced back to December 15 - that's when the Auckland border lifts, allowing those with a vaccine pass or a negative test in the previous 72 hours to leave the outbreak epicentre.
"The opening of the Auckland boundary on December 15 is probably the single most consequential COVID-19 response change before the end of 2021," said Michael Baker, epidemiologist at the University of Otago and perhaps the country's top expert in all things COVID.
"Given the relatively high levels of SARS-CoV-2 virus circulating in Auckland, people leaving Auckland in large numbers over the Christmas-New Year period are likely to disseminate the virus widely across New Zealand.
"This process will probably not result in large outbreaks initially, as the measures now in place across New Zealand - relatively high vaccination coverage, continuing testing and contract tracing, and restrictions on indoor gatherings in hospitality venues - will limit the size of outbreaks.
"However, there will almost certainly be infections and cases of serious illness and deaths, particularly when the virus is introduced into poorly vaccinated families and communities where it will spread easily."
Dion O'Neale of Te Pūnaha Matatini and the University of Auckland said during a typical week prior to COVID-19 or at alert level 1, there were 200,000 trips outside of Auckland - and double that over the Christmas/New Year period.
"Requiring people to be vaccinated, or to test negative for COVID in the 72 hours prior to travel, can be expected to slightly reduce the chance of further cases spreading outside the Auckland region. However, there are a number of reasons why these measures might not be as effective as we would hope."
Firstly, children - who make up almost a quarter of cases in the current outbreak - can't yet be vaccinated, and aren't required to show any proof of a negative test before leaving the city.
"Similarly, a negative test in the three days before travel is not going to mean that adults are still non-infectious when they travel," said Dr O'Neale.
"And while vaccination is great at preventing transmission in general, it can make it trickier to prevent spread outside of a region since it can reduce the symptom severity of breakthrough infections sufficiently that people may not realise that they are infectious when travelling."
He also notes many of the places Aucklanders like to travel over summer also happen to be places with low vaccination rates, like Northland. While some local leaders have begged Aucklanders to visit for economic reasons, others have urged them to stay away for now - especially if they're unvaccinated.
"We hope that a good number of people make the choice to stay in town for the holiday period, possibly delaying their trip until vaccination rates in other areas have caught up with those in the major cities," said Dr O'Neale.
Dr Plank said if the virus gets seeded into low-vaccinated communities, the extent of the disaster might not be clear until after the Christmas/New Year break.
"When schools and workplaces go back next year and heading into the cooler months could be a crunch time when cases may start to rise more rapidly. We need to have a big push on boosters between now and then to keep our immunity levels as high as possible."
Another possibility is that the traffic light system inadvertently creates a chain of transmission amongst the most vulnerable - the unvaccinated.
Aside from the lack of lockdowns, the biggest change the traffic light system introduced was making certain high-risk services inaccessible to the unvaccinated. Some businesses can continue to serve the unvaccinated if they like, but under severe restrictions - such as lower capacity limits or having to operate contactlessly.
A number have sought to attract the unvaccinated dollar, willing to operate under tight restrictions not to lose their custom, while others have shown themselves to be willing to bend or break the rules.
Shaun Hendy, also of Te Pūnaha Matatini, told Newshub the traffic light system at this stage "is an experiment and there is a lot of uncertainty as to how effective it will be".
"As always some of this uncertainty comes from how people behave. If the restrictions on unvaccinated people simply result in displaced interactions that bring unvaccinated people into contact when they wouldn’t have been otherwise, then it might be ineffective, but we will have to see.
"This is why it's important that the Government carefully monitors how it goes over the summer period and especially as we head into Autumn, when many of us will go back to work and school."
It's still early days when it comes to Omicron, the variant picked up in southern Africa in November, but it appears to be much more infectious than Delta.
"That would put an end to the otherwise steady or slowly growing caseload we might expect for Delta" if it got in, said Dr Billington.
Omicron is already in Australia - and remember while the source of the Auckland Delta outbreak was never pinned down, the most likely source was a person in MIQ who'd arrived from across the Tasman.
Matthew Hobb, a senior lecturer in public health at the University of Canterbury, said it's "unlikely it will be our unwanted guest this Christmas", with the border remaining quite tight.
"Although unlikely, should Omicron breach our border like Delta did, it will have to be tackled against the backdrop of trying to manage the current Delta outbreak."
Border restrictions are set to be loosened progressively next year.
Dr Plank said while there's some evidence Omicron might result in generally milder infections on average than Delta, its enhanced ability to spread will cause problems.
"It could still cause more hospitalisations and deaths just simply as a result of infecting more people," he told Newshub. "I think it would be prudent to maintain border restrictions and take all steps to keep Omicron out of the community until more is known.
"We won’t be able to keep Omicron out forever but we might need to buy time, for example for updated vaccines to become available and included in our booster programme if this proves necessary."
It's not yet known whether Omicron will be able to outcompete Delta, but it's already clear the former has an enhanced ability to get around the protections offered by a standard two-dose course of the Pfizer-BioNTech virus. Promisingly, data suggests the booster dose gives recipients similar coverage against Omicron as two did against the original SARS-CoV-2 virus.
How to avoid being a super-spreader
Dr Baker has a couple of tips for Aucklanders wanting to leave the city without their travels being the subject of a 1pm press conference.
Firstly, get tested before you go - even if you're vaccinated.
"Families with children under 12 years of age may be particularly vulnerable to taking the virus with them. They should consider getting children tested prior to leaving Auckland."
Secondly, avoid staying with unvaccinated friends and family, in case you do have the virus. Even better, talk them into getting jabbed now, to give their immune systems time to build up protection.
"Now is the time to have those conversations about vaccination with the people you will be visiting and socialising with. There is still time before Christmas for people to have a vaccine dose or booster if they are eligible."
Failure to heed these warnings "could be seen as comparable to drunk-driving" he said, with "the potential to cause serious harm and death to others".
"This is not the time to let people off with a warning."