First BA.5 case detected
Arrival of another Omicron variant unlikely to change infection rates, expert believes
Health officials yesterday announced the first known case of the Omicron subvariant BA.5 arriving in New Zealand. In South Africa, where the infected traveller came from, BA.5 and BA.4 have been blamed for a new surge in cases.
So what will its arrival mean for New Zealanders? Perhaps not much in terms of immediate infection rates, according to University of Otago epidemiologist Michael Baker.
“It’s not a game-changer — not in the way that Delta and Omicron was,” he told the Herald .
“The starting point is that all of these are sub-variants of Omicron. It’s not a new virus, and the net effect on the population will be similar.
“If anything, numbers across New Zealand seem to be plateauing out. The pattern looks set to continue for the foreseeable future.”
The only reason the new subvariants are seeing the light of day, he explained, is because they’ve evolved to be more infectious.
And the new sub-variants are far more likely to cause re-infections as they become less like the BA.1 and BA.2 variants that have been dominant during New Zealand’s current Omicron wave, he said.
In the United Kingdom, Australia and other places government health officials are now tallying which new cases are re-infections. It’s time for New Zealand to start doing the same, Baker said.
“Re-infections are going to become a much bigger issue, and we need a way to count them,” he said.
Officials said the BA.5 case was detected after the traveller returned a positive RAT test on day five/six after arriving on April 26.
“The person followed all testing and reporting requirements, allowing this new sub-variant to be identified quickly, and has now completed their isolation at home,” the ministry said.
“At this stage, the public health settings already in place to manage other Omicron variants are assessed to be appropriate for managing both BA.4 and BA.5.”
The BA.5 variant is believed to have emerged in January, University of Auckland microbiologist Siouxsie Wiles wrote in The Spinoff last week.
“It’s not clear at the moment whether what’s driving the rise in cases is 1) BA.4 and BA.5 being more infectious, 2) BA.4 and BA.5 having mutations that help them evade immunity even more, or 3) whether everyone’s immunity from the last wave is now waning, making them susceptible to infection again,” Wiles explained.
But it seems “almost certain” waning immunity is part of the problem, she said.
Wiles also noted that Delta tended
to infect lung tissue cells while Omicron and its initial sub-variants seemed to focus more on the nose and throat. But she described a “concerning” potential development with BA.4 and BA.5: the L452R mutation.
“The fact BA.4 and BA.5 now have this mutation suggests they’ll be able to infect those deeper lung tissues,” she explained. “Does that mean these new lineages will be able to cause more serious disease than BA.2? Possibly. What we don’t know is how the L452R mutation will behave in combination with the other mutations BA.4 and BA.5 have. Will they cancel each other out, or will their effects be additive?”
Boosters needed
Regardless of whether the new subvariant ends up being more severe, New Zealand knows through experience that more infectious variants can lead to more deaths and worse health outcomes, Baker said.
“For New Zealand, Omicron has been our most dangerous variant so far,” he said.The nation had just over 50 deaths in the first two years of the pandemic followed by more than 800 since “ferociously infectious” Omicron hit New Zealand.
We will have to keep finding new ways to limit transmission, Baker said.
The best precaution New Zealanders can take moving forward, he said, is to make sure as many adults as possible get their boosters and the child vaccination rate continues to climb.