It points to the need for greater restrictions to manage the risks, according to a study led by Dr Mark Hanly from the Centre for Big Data Research in Health of the University of New South Wales and colleagues.

The study, published on Monday in the Medical Journal of Australia (MJA), looks at eight different scenarios testing various rates of transmissibility, vaccine rollout and the scale of border re-opening.

"The planned re-opening of Australian borders to international travellers increases the risk of introducing new chains of infection and new variants of SARS-CoV-2," Dr Hanly said.

"The health system capacity will still be at risk in the most realistic vaccination coverage scenarios if local chains of transmission are active or the international border is opened while local restrictions on social contact are minimal."

NSW Premier Dominic Perrottet announced on Friday that quarantine requirements and caps for overseas arrivals who are fully vaccinated will be scrapped in two weeks, as of November 1.

Fully vaccinated travellers already in quarantine will also complete their quarantine requirements on November 1, even if it is less than 14-days. Overseas arrivals who are not fully vaccinated will be capped at 210 people per week, and undergo hotel quarantine for 14 days.

The number of visitors welcomed to Australia dropped when the international border closed in March by more than a million in December 2019 to fewer than 7,000 in April, the MJA article says.

It is estimated that 80 per cent total vaccination coverage can be achieved by January 2022, although lags in supply and vaccine hesitancy could delay reaching that target until mid-2022 or later. It will also require vaccinating children under 12, which is still subject to regulatory approval.

Calculations based on higher transmission rates led to a sharp increase in the number of infections, Dr Hanly said. "Political and health system policymakers should not focus exclusively on defining vaccination thresholds at which particular restrictions might be removed," they wrote.

Maintaining high levels of community testing to facilitate rapid detection and isolation of people with new infections will remain essential. Mask wearing may also remain necessary, as well as quarantine protocols that minimise the risks of transmission from travellers into the community.

The easing of restrictions and return of overseas travellers would help reunite families and be a significant boost for the economy, Mr Perrottet said.

"We have reached this vaccination milestone quicker than anyone thought we could, and that is a testament to the hard work of people across the State turning out to get vaccinated.

"Welcoming back fully vaccinated travellers will not only mean families and friends can be home in time for Christmas, it will also give our economy a major boost."

Prime Minister Scott Morrison said the federal government would take a watch and see approach to further easing of the national border.

"We'll see how that goes and then we'll move to the other priorities, which I've already set out as being skilled migration, as well as students to Australia," he said.

"And then we'll move on to the challenge of dealing with international visitors to Australia. So, everything all in good time. We're not rushing into this. We're taking it carefully, step by step. I welcome the decision in New South Wales. It's showing another strong step forward, and I think it enables us to progress."

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