A relative of a Covid-infected cleaner at an MIQ facility has returned a "weak positive" test for the virus.

Covid-19 Response Minister Chris Hipkins and director general of health Dr Ashley Bloomfield have provided the latest details about the Grand Millennium worker, who tested positive last night during routine surveillance testing.

The employee, a cleaner, and their immediate household members were isolating at their home in Auckland last night.

The cleaner visited the Mt Roskill Countdown supermarket in Stoddard Rd on Saturday. The person visited from 3pm to 3.15pm that day.

Anyone who was at the supermarket during that time is regarded as a casual contact. They are asked to monitor their health until April 3. The supermarket has closed for a deep clean "as an extra precaution" and will reopen later today, a Countdown spokesperson said. They couldn't confirm when the store would reopen but said cleaners had started working around midday and in the past deep cleans had taken a few hours.

If anyone starts to feel unwell or develop any Covid-19 symptoms they should call Healthline.

Relative's 'weak positive' result

Hipkins said three family members have returned negative results and one adult relative had returned a weak positive result. This person was to be retested.

A change in alert levels was not on the table at this stage, Hipkins said.

The Mt Roskill Countdown was visited by the MIQ worker for 10 minutes on March 20 - this was the only location of interest so far.

The time of the visit will be confirmed and posted online, Bloomfield said.

The person who tested "weak positive" was "under investigation", Hipkins said.

Bloomfield said the weak positive family member was being retested and the result should be returned later today.

The risk was low to the community, Hipkins said, and genomic sequencing results would be released when they came back.

Contact tracing so far revealed "limited" exposure, he said, and the worker remained asymptomatic.

Public health measures remained as important as ever, including washing hands, coughing into elbows and staying home if sick.

"These are all things every New Zealander can do."

This morning Hipkins said the MIQ worker was "lower risk" because there didn't appear to be many locations of interest or many close contacts.

Since March 1, there have been eight cases at the Grand Milennium, all identified on day zero or day 1 of their stay.

Bloomfield said airborne transmission is a much more likely cause than surface transmission, and previous cases thought to be surface transmission are now thought to be aerosolised transmission.

He said people in MIQ who test positive usually don't spend more than one night at their hotel.

The MIQ worker received both doses of the Pfizer vaccine, the second dose being administered on March 16.

Bloomfield said the cleaner only had their second vaccine a few days before testing positive, and full protection from the vaccine usually took seven days after the second dose.

A vaccinated person has a less chance of ongoing transmission, Bloomfield said.

Effectiveness of the vaccine is continually being looked at, and the key thing is that the vaccine is highly effective at protecting individuals, and protects people collectively when high numbers of people are vaccinated, he said.

The family had not yet been vaccinated.

Bloomfield said the MIQ worker wore a mask at work yesterday and they didn't work three days prior to yesterday.

Hipkins said the infection prevention protocols, including PPE use in MIQ facilities in general, were reviewed regularly. The Grand Milennium was last reviewed in January with some "mild" recommendations.

He said the Government did not have concerns around the way the Grand Milennium was operating.

The MIQ worker was being tested fortnightly, but the last scheduled swab for last Thursday wasn't done and was done on Sunday instead.

Bloomfield said there was a reason for that but didn't elaborate.

The family was being spoken to about being moved to the Jet Park quarantine facility.

Hipkins said the transtasman bubble would see more available MIQ capacity, but more empty rooms would be needed as a contingency.

Hipkins said 38,808 vaccines had been administered as of midnight last night, and 4658 of those were second-dose vaccines.

More than 90 per cent of border workers had received the vaccine, he said.

The number of daily doses are in the low 2000s at the moment and would ramp up, he said.

Hipkins said over 2200 people had completed vaccination training and there was no issue of vaccination workforce at this stage.

He said a person in MIQ was told about a positive test result while on their daily exercise, and the people doing their exercise were then physically distanced on the bus and wore masks.

He said putting any positive case on a separate bus would be looked at once the investigation into that case was finished.

Today is one year since the level 4 lockdown was announced, and Bloomfield said the one thing he would do differently would be to keep a record of what was happening.

He said his memory of the time was "I don't remember people saying 'why'. People understood why. I do recall a sense of relief. There had been a sense of anticipation that things were starting to escalate."

There are three other new cases to report today in MIQ. The rolling seven-day average of cases detected at the border is five. There are 68 active cases in New Zealand today.

There were 2754 tests processed yesterday.