"If the vaccine coverage were lower and with appreciable heterogeneity, there would be much larger outbreaks, with more hospital admissions and deaths, and various forms of lockdown would be required to bring them under control," the report says.

"It is vitally important that we try to achieve the highest possible level of vaccination coverage, and that every effort is made to ensure that particular groups in the community are not left with lower levels of immune protection.

"Our group does not believe border restrictions should be relaxed significantly (beyond current 'bubble' arrangements, as with Australia and the Cook Islands) until the vaccination programme has been fully rolled out."

The report says as part of a "phased reopening" - when New Zealand has more vaccination coverage - quarantine-free travel arrangements could be expanded to include other low-risk countries.

"We recommend that, once vaccination programmes in Australia, New Zealand, and the Cook Islands are well advanced, travel between such 'bubble' countries should be restricted to adults who have been fully vaccinated (and their children accompanying them)."

The report says New Zealand shouldn't underestimate the challenges of regularly importing the virus. It notes while the vaccine will project the majority of adults, New Zealand won't have achieved "herd immunity" like other countries due to our elimination strategy.

"Hence we support the idea that re-opening of the borders in 2022 should start in a carefully planned, phased way - with continuous monitoring and adjustments as needed.

"It is fortunate that New Zealand still has at least six months to prepare for reducing border restrictions because considerable preparatory work is required. For example, decisions need to be made about arrangements for obtaining reliable evidence of PCR testing in the country of departure," the report adds.

If New Zealand was to loosen border restrictions now, it could lead to a "much larger burden of illness and death, as well as disruption of our economy and way of life", the report concludes.

Dr Verrall agreed more work was needed to bolster New Zealand's borders.

"The emergence of the Delta variant has altered both the advice provided and our approach to reconnecting with the world," she said in a statement.

"We need to do more to further strengthen our borders and bolster our health defences, including through the vaccine rollout, before we can safely open the border further, and that will take a little more time to properly prepare."

Chris Hipkins, the Minister for COVID-19 Response, said the Government has already commenced some of the report's recommendations.

"The group recommends preparatory work begins now, including seeking advice on rapid testing at airports, along with a strengthening of public health and social measures, such as expanding health system capability and contact tracing capacity and mandating QR scanning at some types of venues - of which work is already underway by the Government."

Prime Minister Jacinda Ardern will speak about the report at the Reconnecting New Zealanders Forum on Thursday - alongside Sir David, Director-General of Health Ashley Bloomfield, and other health and business leaders.

"We know that people are keen to resume international travel to reunite with friends and family, to carry out business engagements and so on," she said at her regular Monday press conference.

"The Government is equally keen, and we also know the need for minimising lockdowns and keeping New Zealanders safe. We only closed the border to keep COVID out and our ultimate goal is to resume quarantine-free travel when we can, in a way that is safe that continues to keep COVID out."

ACT leader David Seymour has accused Ardern of "talking up" Sir David's report and questioned its purpose.

"As usual, there will be lots of words but no action from the minister of announcements," he said in a statement.

"New Zealand is ready for the next stage of the COVID-19 response. Just don't expect it on Thursday."