A Covid-19 modeller is urging eligible Kiwis to get boosted if they haven't been, amid the growing probability New Zealand could get another coronavirus wave before Christmas.
Professor Michael Plank told the Herald it was possible that wave – expected to come on the back of building surges in the Northern Hemisphere – might even compare with July's.
Cases and hospitalisations already appear to be on the rise in Denmark, Belgium and the UK.
In Germany, where reported cases tripled in three weeks to reach 96,000 on September 29, the country's federal minister of health Karl Lauterbach told media another wave had begun.
Plank said this could be because of a combination of factors, such as people in Europe heading back to school, waning immunity, and a raft of troublesome new Omicron sub-variants.
BA.5 descendant BQ.1.1 has been popping up around the world and indicating its own potential at evading immune antibodies – but it's so new that little is known about it.
Another sub-type, BA.2.75.2, makes up just 1 per cent of Covid-19 cases, but has now been detected in nearly 50 countries – including New Zealand.
It's thought to be nearly seven times tougher for our immune systems to block than BA.5 - and is now considered the most resistant variant seen yet.
Scientists have pinpointed two specific mutations that make it better able to latch onto our cells and infect us: even if we'd already been exposed to its relatives.
In one recent study, Chinese researchers estimated it to be, on average, more than six times more likely to reinfect someone who'd had BA.2 - and 2.7 times more likely to cause a reinfection in a person who'd had BA.5.
Another Swedish study has also indicated virus-fighting antibody levels may be five-fold lower against BA.2.75.2 than BA.5.
While ESR has tracked a slight uptick in New Zealand cases recently, there still wasn't any indication that new variants were already beginning to drive a fresh surge here.
While the removal of border testing had left the picture somewhat less clear, importantly, the latest surveillance data from wastewater sampling hadn't shown any tell-tale shifts in variant activity.
And across hospitals, the most recent sequencing data showed BA.5 making up 87 per cent of samples, followed by BA.4.6 (5 per cent), BA.4 (2 per cent), B.A2.75 (2 per cent) and BA.2 (2 per cent).
"But as these variants become more widespread, this could actually accelerate things a little bit," Plank said.
"So whatever happens in the Northern Hemisphere, I'd expect something similar to happen here – maybe in a matter of weeks."
It remained to be seen what effect open borders, dropped mandates and open borders would have in the next wave.
While increasingly warmer temperatures might play in our favour, Plank pointed out many Kiwis were no longer masking up.
"It's very difficult to predict, but it could be that we see something comparable with the recent July wave we had, in terms of the number of potential cases."
That surge topped out at just over 10,000 daily reported cases in mid-July, before dropping away to between 1000 and 2000 now.
"There's also uncertainty about how this will translate to health impacts and hospitalisations, because we do now have very levels of immunity."
Modellers estimate as much as two-thirds of the population now might have been exposed to the virus, giving them extra immunity on top of that conferred by the vaccine, against severe illness and death.
"But we can't say exactly how this might blunt the impacts of another wave."
Plank urged people to ensure they were up to date with their vaccinations and boosters.
"If you're eligible, it's definitely a good time to go out and get one, because you of course want to have that extra immunity before another wave really takes off."