Opening up the border to vaccinated tourists to resurrect this country's tourism industry could require Kiwis to return to life at Covid alert level 2.5.

That is a future vision floated by director-general of health Dr Ashley Bloomfield when asked whether borders might open before the vaccine rollout finished - scheduled for the end of this year.

If it came to fruition it could provide the financial boom that Kiwi tourism operators need. Pre-Covid, the industry was worth $40.9 billion to the economy.

Prime Minister Jacinda Ardern went a step further than Bloomfield in a pre-Budget speech in Auckland yesterday, when she talked about the possibility of having vaccinated people arriving from overseas before the rollout here was finished.

Ardern's speech traversed territory she had not previously visited; she had talked about the need for everyone to have their individualised armour before the borders could open beyond Covid-free countries like Australia.

The factors the Government will consider for opening up, she said, included how well vaccines prevented transmission between vaccinated people, and whether new variants of the virus were emerging which could cause an uncontrolled outbreak - regardless of how widely vaccinated New Zealanders were.

"While I cannot give you definitive answers on where some of this work will land, I can tell you that we will keep an open mind, listen to the science, and prepare ourselves for the range of different opportunities that may arise."

Prime Minister Jacinda Ardern used a pre-Budget speech to float the idea of opening up to vaccinated travellers before the vaccine rollout in New Zealand was finished. Photo / Dean Purcell

But Otago University immunologist Associate Professor James Ussher cautioned against opening the border before the rollout was complete.

"Once we open the borders, even if it's just to vaccinated people, the virus will come in. If we have a significant portion of unvaccinated people, there is a risk of significant community transmission, which will require public health interventions."

Bloomfield didn't venture into whether the borders could open before the rollout finished.

"There's no doubt that having as much of the population vaccinated as possible is key to us being able to open the border," he said.

"I strongly believe that - even alongside vaccination - we may well need to lift our baseline level of public health protective behaviours as part of our move to open up to a wider group of low-risk countries - let alone beyond that.

"It may well be that we need to be more of a 2.5 level as our baseline, alongside vaccination, as part of the protections we need in place to be able to open the border."

Director of the Immunisation Advisory Centre Dr Nikki Turner agreed, saying vaccines were very effective - but not 100 per cent effective.

"You will still have community transmission with vaccinated people, so going forward we will need to consider going a bit harder with our public health measures.

"We are relatively slack, really, on the use of masks and other public health measures. I think we've got a bit complacent."

The inevitable presence of the virus after borders were opened wouldn't necessarily lead to more Covid deaths, she said.

"A vaccinated person is incredibly unlikely to die and incredibly unlikely to be very sick. So long as a majority of people are vaccinated, and the majority of the people coming in are vaccinated, we should avoid much of any death or severe illness."

How far Covid might spread depended on several factors, including whether there were pockets of lesser-vaccinated communities or areas; Bloomfield this week identified the West Coast, Golden Bay and Northland as places where take-up might be weaker.

Tourism Industry Aotearoa chief executive Chris Roberts expected a risk-based approach to the border to continue.

"There will not be some magical moment when unrestricted global travel can resume," he said.

"Rather, we will need to take a series of small steps, country by country."

But Restaurant Association chief executive Marisa Bidois said level 2.5 - which includes restrictions on gatherings - as the new norm would be a step backwards.

"Our industry is just getting back on its feet after what has been an incredibly challenging year," she said.

"The icing on the cake now will be to get the borders opening so that our tourist destinations and CBDs can get back to pre-Covid business levels. But to do this at level 2.5 feels like a giant step backwards."

Otago University epidemiologist Professor Michael Baker said there were still many "gaps in our critical knowledge" when it came to when the borders should open.

"In particular, the effectiveness of the vaccine and duration of protection, how well it will work against different variants, whether there'll be an internationally-agreed system for vaccination status - and tracking it in a way people trust.

"It's very hard to know how much the comments today advance the debate because there's so many unknowns, but it's very positive that the debate is happening. There's huge complexity, which I think everyone appreciates."

Bloomfield said there might come a point where New Zealand learned to live with Covid-19.

"There's no doubt that in a future - and this is a three- to five-year horizon - as vaccination rates increase around the world and Covid-19 moves to being a more endemic disease, rather than an epidemic or pandemic, it will be in communities or in countries routinely around the world.

"That means that here in New Zealand and other countries, there will need to be really good public health systems in place for identification, contact tracing and follow up - and testing."