Professor Michael Baker says the Auckland border should be treated like an "external border to the world" amid the current Covid-19 Delta outbreak.
The Otago University epidemiologist on Tuesday told Breakfast it wouldn't be until mid-January that all DHBs in New Zealand hit the target to get at least 90 per cent of the population vaccinated. The number was the Government's target before opening up.
So, despite Prime Minister Jacinda Ardern announcing Aucklanders would be able to reunite with family outside the city for Christmas, Baker believes the Auckland border should remain tight if Covid-19 rates continue to climb.
"A key aspect to this is maintaining a very tight boundary around Auckland where there is sustained transmission, the rest of the country is still in elimination mode - if we keep it like that that's hugely beneficial to the country," he said.
"It means that we're going to decrease the number of cases across New Zealand, the economy can keep functioning normally at Alert Level 2 settings - things highly desirable.
"We've got to look at the border around Auckland or the boundary the same way (as people flying into New Zealand) because if there's lots of transmission of the virus in Auckland, as there will be by that stage, we can't have people travelling all around the country while we still have relatively low vaccination coverage.
"This is sticking with the plan the Government outlined for the last month-or-so about how we are going to opening up the rest of the country so it's critical we keep that boundary in tact around Auckland until the whole country is up to 90 per cent fully vaccinated.
"It does meant that unvaccinated people can't travel out of Auckland really from when they obviously move to the traffic light system, and also we have to look at treating that a bit like an external border to the world because that's what it is - you can't have people with this virus taking it all over the country."
His comments come after Air New Zealand on Tuesday morning announced all travellers will be required to provide proof of vaccination or a negative Covid-19 test before checking in to domestic flights from next month.
Baker also told Breakfast that space should be freed up in MIQ so people aren't isolating in big inter-generational homes.
"People flying into Auckland, they could be isolating at home rather than going into MIQ and that way we could free up those spaces in MIQ for people in Auckland who really are getting sick and need to be looked after in a safe environment rather than staying in a multi-generational household, potentially infecting other members of that household," he said.
"This is a really critical source, we should be using it for infected Aucklanders rather than low risk travellers arriving from overseas."