There also weren’t any indications Pirola was causing more severe levels of disease, with BA.2.86 still absent from hospital samples sequenced so far.
Rather, the lineage most identified was EG.5 or “Eris”, accounting for 41 per cent of all variants sampled by the ESR - and about 46 per cent of samples that’ve come from hospitals.
While EG.5 had been recently growing in proportion at a rate of 4 to 6 per cent each day, there were now signs its growth had slowed – meaning it might have reached its limit here, or that other subvariants were becoming more competitive.
ESR considered the top contenders to come in its place were HK.3 - which itself stemmed from EG.5 - or FL.2, one of the many “recombinant” XBB and XBC types making up more than half of all locally sequenced variants.
Each of these hybrid strains has packed some immune-evasion advantage, but only enough to keep slight pressure on case numbers in what’s now a well-exposed, highly vaccinated population.
While the virus continued to cause thousands of infections, hundreds of hospitalisations and tens of deaths every week – and this year may claim twice as many lives as the flu typically does - it’s now been around 10 months since New Zealand saw a significant Covid-19 wave.
On current evidence, Covid-19 modeller Professor Michael Plank didn’t expect Pirola to change that.
“What we’re seeing here is broadly consistent with the picture that we’re seeing internationally,” he said.
“BA.2.86 is spread very wide geographically and appears to have a toehold in lots of different countries, but it hasn’t really shown the ability to grow rapidly in those places where it’s getting picked up.”
Plank speculated that Pirola – designated a “variant under monitoring” by the World Health Organisation – might be finding a “particular niche” in the population.
“Perhaps there’s a sub-group of people who maybe have a slightly different immunity profile – and it’s able to very efficiently infect those, but it’s not doing so well with the rest of the population.”
In any case, it needed to be closely monitored.
“It’s definitely one to keep an eye on, just because it could still pick up some further mutations that allow it to get some growth advantage that it’d need to cause a significant impact,” Plank said.
“At the moment, it’s certainly not looking likely that it’s going to cause a major wave – but it already has a large number of mutations, and it’s possible that it could pick up some additional ones that increases its fitness.”
Otago University epidemiologist Professor Michael Baker aired similar concerns last month.
“The main concern is that it shows how the Covid-19 virus is still capable of big evolutionary jumps, which is a further reminder that the pandemic remains unpredictable and is certainly not over,” he said.
“This new lineage represents an important new branch in the evolutionary tree of this virus that could continue to accumulate mutations that may make the virus more transmissible or harmful in the future.”
Last Friday, Baker and 15 other experts called for a comprehensive new strategy for the next phase of the pandemic – and one to cover all serious respiratory illnesses.
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.
