The only reason the new sub-variants are seeing the light of day, he explained, is because they've evolved to be more infectious. That means they could contribute to the increase in reported cases that Auckland and other regions are starting to see, he said.
Another issue, he said, is that 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.
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.
South African surge
Officials said today that the BA.5 case was detected after the traveller returned a positive RAT test on day five/six after arriving from South Africa on April 26.
Whole-genome sequencing was conducted after a PCR test was administered the following day.
"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 of Health said today, adding that the sub-variant's arrival was not unexpected.
"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."
There were 5647 new community cases of Covid-19 and three Covid-related deaths reported in New Zealand today.
Meanwhile, in South Africa, cases have increased sixfold - edging near 10,000 per day - in just the past two weeks, according to UK publication The Telegraph. Scientists there believe the BA.4 and BA.5 offshoots could be responsible and last week World Health Organisation leader Tedros Ghebreyesus confirmed as much, the newspaper reports.
Ghebreyesus also emphasised that it's not yet known whether the new sub-variants will cause more severe disease than previous Omicron sub-variants.
Concerning development
The BA.5 variant is believed to have emerged in January, University of Auckland microbiologist Siouxsie Wiles wrote in
a piece for 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 sub-variant ends up being more severe than its predecessors, New Zealand knows through experience that more infectious variants can lead to more deaths and worse health outcomes, Baker said today.
"For New Zealand, Omicron has been our most dangerous variant so far," he said, noting that 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 should never describe it as a mild infection."
As new variants and sub-variants arise and get better at evading immunity, 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.
"It just becomes even more important," he said.
