Coronavirus: Ashley Bloomfield says COVID-19 'must have' come through the border, Jacinda Ardern remains unconvinced

While the Director-General of Health thinks the latest COVID-19 outbreak "must have" come through the border, the Prime Minister says there's still no evidence of that.

After 102 days seemingly free of the virus at alert level 1 - the least restrictive of the four-step system - the country was plunged back into level 2, and Auckland level 3, just over a month ago. While Auckland has since moved to a hybrid level 2.5, the rest of New Zealand remains at level 2, with new cases still being found.

Luckily they all seem to be linked to the same outbreak, suggesting a single introduction of the virus, which has killed at least 930,000 people worldwide this year.

But genome testing and contact tracing haven't linked the cluster to any of the infections picked up at the border in managed isolation and quarantine facilities (MIQ).

"It is still a mystery, isn't it?" Director-General of Health Ashley Bloomfield told The AM Show on Tuesday.

"We are very confident it hadn't laid dormant in the community as it were. It must have been introduced through the borders, either at the airport, or at a managed isolation facility, or possibly through one of the ports."

But Prime Minister Jacinda Ardern, appearing later on the show said there's still "no evidence of that".

"We did a sweep of testing across all those frontline border workforces, across the port, across all our managed isolation facilities. You'll know that we also genomed everyone that was in our MIQ to try and find matches there. We did not find the source."

New Zealand isn't alone in having an outbreak with no obvious source, after successfully seeing off the first wave of the pandemic.

Vietnam, which has a population 19 times higher than ours and shares a border with China - where the virus originated - has only had 1063 confirmed cases. It went 99 days without any community transmission of the virus - only a few days shy of New Zealand's record - before a 57-year-old man tested positive. He hadn't left his home town of Da Nang in months.

"Look, that's not uncommon," Ardern said of the mysterious reappearance of the virus in New Zealand.

"I've looked at other countries - Vietnam being one of the most recent. After 99 days of no transmission they had an outbreak - they still haven't found the source. So it was not for trying. We wanted to know where it came from so we could tighten up those provisions, but the honest truth is we may never be able to answer that question."

The good news is there doesn't appear to be a second separate cluster of cases, meaning there was likely only one breach of the border - if that's what happened.

Jacinda Ardern.
Jacinda Ardern. Photo credit: The AM Show

Dr Bloomfield says work is still ongoing to find the source, in case it reveals a weakness in the MIQ system.

"At the moment, we haven't been able to find a match between a genome on this virus and any of these previous cases in our managed isolation facilities. But ESR are continuing to test samples and just compare those against this particular version of the virus. We are hoping we can still find out where it happened because that is the key to then seeing if there are any loopholes we need to close."