That compared with the mere seven cases – or just 0.01 per cent of the population - reported in the region up until January 23.
Similar changes were observed elsewhere.
Toward the end of January, just 29 cases had ever been reported in Hutt Valley; by last weekend, nearly 20 per cent of a population of more than 156,000 had been reported as active cases.
Before Omicron hit, no DHB area had ever had more than one per cent of their population reported as cases – and per capita rates in some, including Capital and Coast, Canterbury, Wairarapa, Hawke's Bay, Whanganui and Mid Central, were less than 0.04 per cent.
Those proportions had since climbed to between 15 and 20 per cent.
Counties-Manukau, which had the country's highest per capita case rate before Omicron – 0.9 per cent of its 578,650 population being ever active – now had the second-highest, or 21.37 per cent.
Covid-19 modeller Professor Michael Plank said the comparisons showed a "stark difference".
"Before Omicron, we had very, very low levels everywhere, with the slight exception being Auckland – but even there, pre-Omicron numbers were a tiny fraction of what they are now," he said.
"It's almost like looking at two completely separate epidemics."
Plank pointed out reported cases only accounted for a proportion of actual infections – and perhaps just one in three.
"That would put Tairawhiti's cumulative attack rate at about 60 to 65 per cent," he said.
"That's high, but it's not inconsistent with what other countries have estimated in their own Omicron waves."
He also noted that per-capita case rates across regions didn't always translate to heavier health burdens, given local age structures and a range of other demographic variables could change the picture.
Tairawhiti's hospitalisation rate, for instance, had been among the lowest in the country.
Hauora Tairāwhiti chief executive Jim Green said his region also had the youngest DHB population of any in the country – and the virus had spread more among younger people.
"The spread of the cases across our population shows a marked shift to the younger population."
Higher case rates could also reflect higher levels of testing and reporting, and Green said local iwi providers had worked with the DHB to get rapid antigen tests into the community.
"This dichotomy between high case rates and low hospitalisation has been the subject of review for the factors which have contributed to this outcome so far for our community," Green said.
Plank said another obvious point to consider was the fact the Omicron wave wasn't yet over – and areas like the West Coast were still reporting comparatively high case counts.
"We may have reached the 'peak' in cases but the virus is still in high circulation throughout New Zealand and our DHBs hospitals and staff are still under pressure," University of Canterbury public health lecturer Dr Matt Hobbs said.
While the picture was complex, the difference in case counts before and after the Omicron wave showed how widespread the virus had now become.
"While it is clear there are some differences in magnitude by region, the increase in numbers affected is rather striking," said Hobbs, who co-directs Canterbury's GeoHealth Research Laboratory.
"It also highlights how some areas have been more affected by the Omicron outbreak than others and thus will have been put under more pressure due to the sheer number of cases."
Work by Hobbs and colleagues has also underscored regional disparities in health – something that wasn't clearly reflected by looking at case rates alone.
"While the variation by DHB is a complex picture, one clear and important aspect is timely access to the vaccines," he said.
"We know that evidence has shown that Māori, over 65-year olds, people living in areas of high socioeconomic constraint, and rural residents have worse access to vaccination services."
Another important factor was how comparatively connected DHB areas were, with some having a higher risk of spread through having more schools and workplaces.
"They also have different profiles in terms of their vulnerability to infectious diseases in terms of number of people living in an area with long term health conditions for instance," Hobbs said.
"Our research previously showed that high potential transmission risk and high health vulnerability were identified in several areas of the North and South Island, including in Christchurch, Hamilton, Dunedin and Auckland.
"Now though, we also have the added complication of prior infection especially in areas like Auckland which may be providing some protection as people will have already been infected and recovered from Covid-19."
