Prime Minister Jacinda Ardern has hit back at Opposition leader Judith Collins for "trying to imply without any evidence" that the latest COVID-19 outbreak came from the border.
Collins told The AM Show on Wednesday the outbreak has "obviously been caused by a border mishap", and she doubled down in Parliament by quoting Otago University Professor Nick Wilson who said "we must have had some failure at the border".
Ardern hit back at Collins in Parliament by reminding her that there is no evidence yet to link the south Auckland cluster to the state-run managed isolation and quarantine (MIQ) facilities where returnees and COVID-19 cases are housed.
"I agree with him that it is unlikely that there could have been silent transmission for that long.... analysis supports that to date. However, that does not necessarily mean there has been a failure at the border," Ardern said.
She pointed to Hong Kong, Singapore, Korea and the Australian states of Victoria and New South Wales as jurisdictions that have experienced resurgences in COVID-19 despite being hailed for managing the virus well.
"I note Vietnam reached 99 days and has been highly praised for their proactive and rigorous regime. They are yet to determine the source of their outbreak either," Ardern said.
"This does not mean anyone has failed. It means perfection in the response to a virus in a pandemic is just not possible."
The south Auckland cluster is understood to have originated at cold storage facility Americold in Auckland but the source is still unknown, and Ardern said there are a "number of ways" the virus could have entered New Zealand.
"To date we have not established the source of the cluster but we are working hard to investigate all possible options," she said, although Director-General of Health Ashley Bloomfield has all but ruled out transmission from cold store goods.
"No one wants to find the source more than we do," Ardern said. "It helps us make sure that we have got all of the periphery of this cluster. But it is not evidence-based to imply it has come from one particular origin when we have not defined that as yet."
Collins has suggested the virus outbreak is linked to the border after Newshub revealed more than 60 percent of border-facing workers had not been tested the week before the latest outbreak, falling short of Cabinet's approved testing strategy.
She quoted Auckland University Professor Des Gorman who told Newshub he thinks New Zealanders "deserves better than such a casual approach to surveillance to possible infectivity among the border workforce".
The Government has since ordered all border-facing staff to be tested.
"I again point to the fact that the vast majority of our border staff have been tested and to date we have not found the source of this outbreak," Ardern said in response.
She pointed to research by ESR, New Zealand's Crown Research Institute, which has been helping efforts to understand COVID-19 by performing whole genome sequencing on positive coronavirus samples.
"The ESR evidence demonstrates that the genome sequencing suggests that the source of this outbreak was in very close proximity to the first cases, thus demonstrating that it's not a matter of there having necessarily been a case that was not picked up," Ardern said.
"Of those tests we've been able to run we have not been able to demonstrate a link between the genome sequencing of this cluster and those to date where we've had the ability to test who have come through our MIQ.
"We will continue looking, but it is simply not fair to say that this has been illustrative of a particular failure when there is no link to our borders or anywhere else at this stage."
The latest Ministry of Health data shows there are 2422 close contacts of the current cluster, of which 2368 have been contacted and are self-isolating.
The total number of active cases in New Zealand is 134, of which 21 are imported cases from MIQ facilities.