Te Pūnaha Matatini Covid-19 modeller Professor Michael Plank has welcomed the Government's plan to keep Northland in red, saying the region is at risk of Covid-19 spread.
On Monday Prime Minister Jacinda Ardern announced Auckland and other regions in red excluding Northland are set to move into orange at 11.59pm on Thursday, December 30.
"Cautious optimism" is how Ardern described the city's falling Covid case numbers under the traffic light system while announcing the shift.
Plank agreed with the Government's decision to move regions into orange.
"Provided that cases remain relatively stable I think moving into the orange setting will be a reasonable move."
Immunologist Dr Dianne Sika-Paotonu said with more New Zealanders interacting and getting out, there's a risk that this will promote and accelerate spread.
"Care and caution will still be needed moving forward as Delta continues to spread across the country," she said.
Cabinet undertook its first review of the new Covid-19 framework on Monday, Ardern said, and it had been encouraging to see a decline in cases.
Other regions at red now have an additional period of time for second doses to be administered, Ardern said. Those areas won't reach extremely high rates of vaccination until mid-December, she said.
Ardern acknowledged enormous progress had been made in Northland but said they must be cautious.
Plank was not surprised by the Government's move to keep Northland in red as the region has the lowest vaccination rate.
With the summer holidays just around the corner, he believes rural and vulnerable Northland communities are a risk of Covid-19 spread.
"It's quite a popular destination for holidaymakers over the summer period and that could lead to lots of Covid being brought in to those vulnerable communities."
Ardern said that Northland was 4000 shots shy of meeting a 90 per cent first-dose target. She said the difference between Northland and other regions is those few thousand vaccinations. The decision to keep it in red is about being cautious.
The next full review of the traffic lights will be on January 17.
When asked why Auckland could not move into orange as soon as possible, Plank said the effects of the new traffic light system are not known yet.
"Obviously it has been a very big change for Auckland with bars, restaurants and cafes opening," he said.
"We need to check that isn't going to produce [a] big increase in the number of cases."
Monday's decisions come two days before Auckland's boundaries are due to reopen - from Wednesday people can move in and out of the city if they are vaccinated, or have a negative Covid-19 test.
Sika-Paotonu said the country's high vaccination rate is due to the hard work, sacrifice and dedication of many New Zealanders, but believes that must continue.
"It is important that this work is supported to continue moving forward, to keep everyone safe from Covid-19, especially our most vulnerable."