Tricky new Covid variant on the rise as NZ’s sixth wave approaches peak

The latest Ministry of Health figures showed there’d been 5230 reported cases of the virus over the week to June 9, along with 354 cases in hospital and 20 virus-attributed deaths. Photo / WHO

New Zealand’s sixth Covid-19 wave is likely close to its peak, a modeller says - but a tricky new variant already accounting for a third of cases could see it roll on into winter.

The latest Ministry of Health figures showed there’d been 5230 reported cases of the virus over the week to June 9, along with 354 cases in hospital and 20 virus-attributed deaths.

After a sharp rise in case numbers and the virus being detected in wastewater over May, there were some signs the wave was now beginning to slow - or had at least reached a plateau.

“Hospitalisations have continued to rise, but at a slower rate than they were doing a few weeks ago,” Covid-19 modeller Professor Michael Plank said.

“I think it’s likely the wave is close to peaking, but it’s a bit too early to say for sure.”

Plank singled out three key drivers behind the mid-year bump.

Wastewater sampling (marked in green) and case reporting (blue) shows national Covid-19 activity has been elevated since the beginning of May. Source / ESR

One was that the population’s immunity to infection would have waned over the six months since the last flare-up around Christmastime; another was colder weather keeping more Kiwis indoors.

“While this may not be the main driver, it probably means the wave is a bit larger than it would be if it was happening during the summer months.”

The third was the latest generation of Omicron variants, namely the sub-type KP.3, which appears to have emerged dominant from a soup of circulating strains dubbed “FLiRT”.

Scientists have so far singled out two key changes in KP.3′s spike-protein - which the virus uses to break into our cells and infect us - that’d likely given it an extra edge over its parent variant, JN.1.

“Some of the mutations in these new variants are involved with immune evasion, and some are probably associated with binding to cells,” ESR’s genomics and bioinformatics science leader Dr David Winter said.

“Those are two things the virus has got to do to infect us.”

The Omicron subvariant KP.3 - shown here in pink - made up around a third of the different coronavirus variants recently sampled in wastewater. Source / ESR

While JN.1 was a major player in our last wave, responsible for more than three-quarters of cases at its peak, a fast-rising KP.3 already made up just over a third of recently sequenced cases.

“So, it’s going to keep on transmitting, and will probably keep pressure on case levels,” Winter said.

“Anecdotally, I know more people with Covid at the moment than I can remember any time recently.”

Winter added while the virus was always evolving to get around our immune defences, there was at least no indication KP.3 was making people sicker than its Omicron predecessors had.

Otago University epidemiologist Professor Michael Baker said it was nonetheless worrying to see waves reoccurring relatively frequently, given each reinfection brought its own risks.

“It looks like the whole country is going to be very exposed to this virus over the next few weeks,” he said.

“We can hope that this peak may recede, but if it’s being driven by new subvariants that we have less immunity to, then there’s no single force that will drive case numbers down.”

Adding to the pressure on the health system was a winter flu season getting under way.

“We’re perhaps still a little way off from the typical peak of flu, which can really be any time from now through to September, but we’re now very much in that more intense part of flu season.”

Baker was pleased to see the Government commit to continue supplying Covid-19 vaccines, antivirals and tests, but pointed out New Zealand still lacked a comprehensive strategy to manage respiratory diseases.

He encouraged people to get their vaccinations if they were overdue - and to stay home if sick.

“Even if you feel pressured to go back to work, just think of other people, and don’t do it.”

Meanwhile, a newly published genomic study has shown why homes are also major hotspots for spreading Covid-19.

The study focused on 71 households in 2022, over the months in which Omicron first washed through the country with its BA.2 and BA.5 variants.

Genomic analysis showed with BA.5 in particular, a single infection brought into a home could come with a roughly three-in-four chance of other household members catching the virus.

Study author and Otago University virologist Professor Jemma Geoghegan said given our immune landscape had changed much since, that “attack rate” within homes today might not be as high.

“But as we’re entering winter, with other respiratory diseases like RSV about, I think it highlights the important role that households play in transmission - and dissemination back into the community.”

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.