Dr Ashley Bloomfield says a vaccinated New Zealand could open the borders to more countries, but alert level 2.5 might then be the new normal.
The director-general of health made the comments during a media briefing today in response to whether the vaccine rollout would need to finish before the borders could open beyond safe travel zones like Australia.
"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," Bloomfield said.
"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.
"There's no doubt that having as much of the population vaccinated as possible is key to us being able to open the border."
At a pre-Budget speech in Auckland today, Prime Minister Jacinda Ardern's laid out some of the Government's thinking about how the borders can reopen.
She has previously said the borders would have to stay closed until Kiwis had been vaccinated, except for countries with no Covid such as Australia and - from next week - the Cook Islands.
She said today that vaccinated people from overseas might be able to come to New Zealand before the vaccine rollout was finished.
The factors to consider, 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 vaccinated New Zealanders were.
Bloomfield added other considerations, including population vaccination rates and how much transmission there was in the country in question.
Opening the border to a country with high rates of vaccination as well as community transmission would likely lead to the virus being imported into New Zealand, he said.
"Even with a very highly effective vaccine like Pfizer, which has 95 per cent efficacy against symptomatic Covid-19 , that still means for every 1000 people travelling from that country who might be fully vaccinated, there'll be 50 of that 1000 who might have got infected."
There would likely be a point in the future where New Zealand diverged from elimination and lived with Covid-19, he said.
"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 really good public health systems in place for identification, contact tracing and follow up - and testing."
For now, Bloomfield said, vaccination was secondary to keeping the virus out of the country.
There might be disruptions to the supply of Pfizer vaccines that are due to arrive in larger numbers in July, he said, but so far the supply had been uninterrupted.
Contingency plans were to use the other vaccines if necessary, but Bloomfield said the plan for now was still based fully on the Pfizer vaccine.
The rollout plan could also accommodate an additional 250,000-odd 12- to 15-year-olds - potentially in schools - should MedSafe approve Pfizer for that age group.