A heavily-mutated Omicron subvariant causing a global stir is yet to pop up in New Zealand – but an ESR scientist expects it’s just a matter of time before it’s detected here.

Health authorities are still trying to assess what BA.2.86′s striking number of mutations – setting it far apart from its closest relative and roughly in line with Omicron’s genetic difference to its predecessor – means for its ability to spread or make people sicker with Covid-19.

Already confirmed in the US, UK, Denmark, Israel, Switzerland and South Africa, “Pirola” has been tagged a “variant under monitoring” by the World Health Organisation, while a top UK expert panel has concluded there’s “established international transmission” - and potential for rapid growth.

So far, regular sampling and sequencing of Covid-19 hasn’t turned up Pirola in Aotearoa, ESR’s pathogen genomics technical lead Dr David Winter said, but that was likely to change soon.

 “New Zealand is entirely connected to the world and if something is circulating at an appreciable level, we’ll get it eventually.”

Each week, ESR produces results for about 100 to 200 virus genomes sequenced from clinical samples.

Assuming about 150 samples were sequenced weekly, there was a 95 per cent chance of detecting a variant circulating at 2 per cent frequency – and a 99.9 per cent chance of recording one that made up more than 5 per cent of cases.

But Pirola was likely to be spotted even sooner through wastewater surveillance, which currently screened just over half of the population.

 “We’ve been watching international observations with a great deal of interest and it’s quite interesting that it seems to be everywhere at the moment, but at a low level,” Winter said.

“So, it’ll be interesting to know how well it will grow.”

For weeks, Covid-19 surveillance through wastewater sampling, together with community and hospital screening, has shown the presence of another new subvariant that’s been driving surges in the US: EG.5 or “Eris”.

“Over the last six weeks, it’s consistently grown as a proportion of all sequenced cases here, and now makes up about 20 per cent of cases,” Winter said.

“We estimate that it’s got a six per cent per day growth advantage, which means that it’s just going to keep contributing to an uptick in case numbers that we saw begin before the end of isolation rules.”

By next month, it could account for as many as half of sequenced cases.

Still, in a population now well exposed and highly vaccinated, Winter said it wasn’t expected to fuel a wave like 2022′s mid-year surge.

Globally, New Zealand and Australia continued to stand out for their unusual variant profiles.

For months, the coronavirus circulating in both countries has been dominated by a group of immune-evasive “recombinant” lineages called XBB and XBC, of which EG.5 was an off-shoot.

“We’ve had a slightly different experience than the rest of the world, which has been interesting, and until recently, we’ve had a period with these XBB variants where case numbers were gradually declining,” he said.

“That appears to have changed when we got EG.5, which has been quite common overseas and has a few additional mutations in the spike protein.”

Just how much of a splash Pirola would make here remained to be seen.

“But when it does get here, it will have to compete with EG.5 and the rest of these very successful XBB variants, which have high transmissibility and have really fine-tuned how to infect people.”