Covid 19: Will NZ’s wave peak before summer holidays?

The Ministry of Health is continuing to report thousands of fresh cases. Image / NIAID

New Zealand’s ongoing Covid-19 wave could peak by New Year, with fewer than 10,000 daily infections – but much of that hinged on how Kiwis behave ahead of Christmas, a modeller says.

The Ministry of Health is continuing to report thousands of fresh cases – around a quarter of them reinfections – as the country moves through the second of two over-lapping, late-year bumps.

As at Monday, when 6000 new daily cases were registered, the rolling seven-day average stood at more than 4040.

That was around 1000 more than the average at the start of October, and three times what it was at mid-September, when the Government announced the end of widespread masking and other measures.

Since then, Covid-19 modeller Dr Dion O’Neale said, New Zealand had seen an initial wave powered by behavioural factors – namely fewer Kiwis wearing masks – followed by another driven by a mix of co-circulating subvariants.

“If we didn’t have that behaviour-induced bump, we’d expect the current wave to keep going up but be on its way down by Christmas,” said O’Neale, of Covid-19 Modelling Aotearoa.

“Having had that bump might delay things and spread our current subvariant-induced wave out over a slightly longer period.”

While he expected the peak wouldn’t top 10,000, and likely arrive by 2023, more people socialising at pre-Christmas events and functions could change the numbers.

“We could actually see a small peak in cases if people decide, I’ve had enough, I’m not going to test before going to the Christmas party, and if I do know the result, I’m certainly not reporting it.”

On the other hand, schools breaking up, and workers leaving for the holiday period, would provide a “circuit-breaker” to help drive cases down.

“Generally, we think the peak won’t be quite as high as what we saw over the June and July wave, but also not much lower than it.”

Because of factors like asymptomatic transmission and fewer people seeking tests or reporting results, modellers faced what was likely to be a large hidden picture of infection.

O’Neale figured our current case ascertainment rate (CAR) – that’s the ratio of confirmed infections to missed ones – was sitting at about half of what it was earlier in the year.

While officials recently warned of a summer wave reaching 11,000 daily cases, O’Neale noted this was working off older CAR parameters and assumptions.

“It’s possible that people might get better at reporting cases if they’re seeing Covid-19 in the news more – but otherwise, we’d expect [the CAR] to be a bit lower than what was used to model that 11,000 figure.”

He and others have long been calling for community prevalence surveys that would reveal New Zealand’s infection iceberg, yet, after repeated delays, the Government now wouldn’t be launching one until next year.

“For us, this is the big unknown.”

O’Neale encouraged people arranging or attending functions to venues that were outdoors or otherwise well-ventilated, and to stay away and get tested if experiencing any symptoms.

“Just opening doors and windows can make a huge difference.”