Coronavirus: How many might already be infected in the latest Auckland COVID-19 outbreak?

If Auckland's new COVID-19 case can be linked to the recent Defence Force cluster, it's likely we'll have fewer than 10 cases and won't need to go into lockdown, an expert says.

A student who lives downtown tested positive for the virus this week, with no obvious link to any previously known cases. Tests have suggested a potential link to the cluster that emerged earlier this month, after a Defence Force employee based at the Jet Park quarantine facility in Auckland contracted it. 

University of Auckland COVID-19 modeller Shaun Hendy, who's been advising the Government on its response to outbreaks, told The AM Show on Friday if the new case is linked to the Defence Force cluster then a lockdown probably won't be necessary.

"It's all going to depend on how the analysis pans out. It sounds like they've got a likely link to the Defence Force cluster that turned up last week. If that's the case, then we're probably looking at a much smaller outbreak than the Auckland August cluster.

"The concern is when we see one of these cases crop up in the community and we can't link it directly to the border, that we're really looking at the tip of the iceberg - so you're looking at dozens and dozens of cases."

That's what happened in August. Four cases of unknown origin were discovered, plunging Auckland back to alert level 3 restrictions. Right away Dr Hendy said it was likely there were at least "five to six dozen" people already infected when the initial four cases were found, perhaps more - with no direct links between them and border facilities or overseas travel suggesting they'd caught it off others in the community, who were perhaps asymptomatic or didn't get tested. 

Shaun Hendy.
Shaun Hendy. Photo credit: The AM Show

Dr Hendy's modelling was proved correct - by the time the August cluster had been stamped out, there had been 179 cases. This time around, if the Defence Force cluster link can be confirmed, it's likely to be about a dozen - perhaps fewer.

"There may well still be some downstream cases - that's a possibility, coming out of people who visited the store on High St or came into this latest case otherwise - those cases may still play out. But we're looking at probably 10 or so, and if we're lucky, less than that."

Epidemiologist Professor Michael Baker told RNZ on Friday morning the person "must have got infected from somewhere", and the length of the chain of transmission was unclear.

"There could be a number of cases. It's much more like the Auckland August outbreak that we had that was quite hard to control. It took a few weeks."

Contact tracing will play a big part in stopping the spread of the virus - if all potential carriers can be identified and isolated, a wider lockdown might be avoided. 

But a Newshub reporter on the ground in downtown Auckland on Friday morning saw several residents of the building where the new case lives coming and going freely, despite officials urging them to self-isolate. 

"We just did the test yesterday and we were told 'isolate yourself, don't go to work until you get your results' so we're waiting for that today," one resident told Newshub. 

"We confirmed with the person who was doing the test, and they said they can't stop anyone from going in or out."

COVID-19 response minister Chris Hipkins said they were relying on "goodwill" at this stage.

Dr Hendy said people "might have very good reasons why they do need to leave the building", and urged the Ministry of Health to get a public health official on site to check with people leaving the building.