Covid-19: Is NZ in for another Christmas wave? Modellers watch for early signs

• A modeller says there are early signs that Covid-19 activity is ticking back up – but it’s too early to tell if that’s toward another summer wave
• New Zealand has seen early summer spikes in coronavirus activity – peaking around Christmas – since Omicron arrived at the start of 2022
• The possible uptick comes after the arrival of new Omicron variant XEC, which doesn’t appear to be making the same splash past ones have

Covid-19 modellers are closely watching for early signs of an uptick toward another summer wave, as a recently arrived variant gradually gains a foothold in New Zealand.

Early summer bumps in Covid-19 activity – along with mid-year waves – have been an unwelcome pattern since Omicron began widely spreading in early 2022.

Each has come with peaks in hospitalisation numbers just days before Christmas, although these holidaytime surges have been growing smaller over time.

Last month, activity ebbed to the lowest levels observed in the Omicron era, but there were now early indications numbers were on the way back up.

Hospitalisation numbers have risen slightly since mid-September, as have national levels of the virus detected through wastewater testing.

Modeller Professor Michael Plank said that given virus activity fell so low last month, it wouldn’t be surprising if it began to increase from here.

“And there are signs in the data that this is beginning to happen,” he said.

“Whether this leads to a summer wave is a bit early to say – but it’s certainly possible.”

Plank said Covid appeared to have settled into a two-wave-per-year pattern – one in early summer and one in early winter – because of factors like waning immunity to reinfection, the evolution of new variants, and seasonal effects like changes in social contact patterns.

“I suspect this trend will continue and is partly due to Covid being more infectious, compared to influenza and RSV, which typically cause one wave per year during the winter,” he said.

“Importantly, two waves per year doesn’t mean that everyone is being infected twice per year.”

The emerging signals come as ESR surveillance recently detected the first cases of XEC: the latest in a succession of Omicron variants packing new immunity-evading advantages.

ESR’s genomics and bioinformatics science leader Dr David Winter said the variant now made up 10% of sampled cases and was “growing steadily”.

Still, Winter said XEC only appeared to have a “moderate” growth advantage over other variants – and much less than what JN.1, which fuelled last summer’s wave, had over its predecessors.

Plank said this suggested that, if XEC did become the next dominant variant, it wasn’t likely to trigger a particularly large wave.

“It is possible a different, more competitive variant will come along before the end of the year, but there is no sign of this at the moment.”

He added that, overall, rates of hospitalisation and mortality remained well down compared to where they were in 2022 when most people in New Zealand got infected for the first time.

“The reason is that most people have hybrid immunity – a combination of being vaccinated and having been previously infected,” he said.

“This doesn’t provide lasting protection against being reinfected, but it does mean the risk of serious consequences is far lower.”

There were around 2800 Covid-attributable deaths in 2022, 1000 in 2023, and, based on current trends, around 750 were likely for 2024.

“For comparison, influenza is estimated to cause somewhere between 200 and 1000 deaths per year, depending on how severe the flu season is.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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