Covid-19 Response Minister Chris Hipkins says the source of the first community case that plunged Auckland into lockdown may never be found - although officials are looking at a potential new clue.

Hipkins is promising to leave "no stone unturned" when it comes to searching for the source of case A – the woman who works at LSG Sky Chefs in Mangere.

It comes as the first Covid-19 vaccine jabs will be given in New Zealand today - nine days shy of a year since the country's first confirmed case. The first people immunised will not be border workers or their families but vaccinators - the people with the important job of administering the shots.

Director general of health Ashley Bloomfield yesterday said there is a new lead in the search for how Covid-19 again found its way into the community.

Officials have found a "possible" similarity between case A's sequence and that of someone who stayed at the Four Points by Sheraton MIQ facility in Auckland.

But even this theory is considered "very unlikely" by Bloomfield, who said the most likely scenario is the case was contracted at the border.

"The airport precinct seems the most likely route of infection – we just need to get to the bottom of how [the LGS worker] has been exposed."

Because of this, he confirmed yesterday that officials were investigating if mingling staff at a canteen at Sky Chef could be linked to the initial outbreak.

That means, according to Bloomfield, 444 other people working around the area of Sky Chef are of interest to the Ministry of Health, including people working at the site, as well as contractors who bring laundry and food to and from the airport.

So far, there are 350 negative tests with 93 still to come.

No new community cases of Covid-19 were announced yesterday.

"[This] does provide continued reassurance that the swift response to the system continues to be highly effective in response to the Auckland February cases," Bloomfield said.

And Hipkins is striking an optimistic tone about the likelihood of any future lockdowns resulting from the outbreak.

"We have demonstrated that we can contain Covid-19 without the need to escalate alert levels."

He said alert levels would only be escalated if there were extra risk factors which officials were not able to quantify or control.

All 31 close contacts from Papatoetoe High School have returned a negative result – aside from the one case revealed yesterday.

About 1490 are considered casual plus contacts at the school – but so far, 1398 have returned negative results with 91 still to come.

But Hipkins has admitted there was "absolutely" a possibility that the Government never finds the source of the outbreak.

He pointed out that the source of the August community outbreak was also never found.

"We might not be able to get to a point where we say, 'actually, this is what we think is the most likely [source]'."

Meanwhile, Auckland University Professor of Medicine Des Gorman has criticised what he says was the Government's lack of clarity around shifting the alert levels.

"Certainly, if you take Sunday, for example, if we need to be in level 3 – and you and I would say that was a reasonable response to the unknown at the time – then how on Earth did they let the Big Gay Out and the America's Cup go ahead?"

But Hipkins defended the Government's moves.

"People can have confidence in the decision that we've taken, because of the extensive level of testing that we have seen and the fact that we have been able to identify the close contacts."

Hipkins acknowledged Sunday's lockdown came into force quicker than previous alert level movements "by design".

"Where we do want to use a short, sharp shock we do want to do that as quickly and efficiently as possible."

Officials are preparing for tomorrow's vaccine rollout to frontline Covid-19 workers.

Hipkins said health workers have been doing "dry runs" to stress test the system to identify any gaps.

"There will be challenges and logistics – but the systems that we have set up are robust and flexible."

The test runs included a number of scenarios such as how the vaccines will be dropped and what should happen if a vial is dropped.

"Human beings are not 100 per cent perfect – people make mistakes," he said.

Hipkins confirmed the Government has a "contingency" that accounts for some vaccines being dropped or wasted other ways.

That contingency was roughly 15 per cent when the vaccines were ordered but Bloomfield said, given the "dry runs", he is not expecting waste to reach that level.