Joint research conducted by the CSIRO and the Queensland University of Technology found that without international travel restrictions, more than 48,000 Covid cases would likely have entered Australia between January and May 2020.

The border control measures meant there was an 88 per cent reduction in internationally acquired Covid cases, based on modelling, with there being 6000 cases recorded in the five-month period that were acquired from overseas.

It's the first time such a model has been used to accurately measure the number of Covid cases imported from all nations globally into a single country.

Researchers hope the modelling tool could help the federal government in determining when to ease border restrictions and reopen international travel once the Covid situation in Australia subsides.

The CSIRO's director of health and biosecurity Rob Grenfell said the border closures in the initial stages of the pandemic were a critical health measure.

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"There have been some public health measures that have been instituted since the pandemic that have had a lot of criticism, and border closures have been one of them," Dr Grenfell said.

"This gives us solid evidence that it has had a significant effect, and we otherwise would have seen seeding of the virus into the country."

Before a total international travel ban was implemented in 2020, border bans were put in place for countries deemed to have been a significant Covid risk.

The study examined the effect of the individual travel bans among the countries that were earliest hit by the virus, including those on China, Iran, South Korea and Italy.

Research found the bans led to a 94.45 per cent reduction in Covid cases arriving in Australia from China, a 94.41 per cent reduction of cases from South Korea, 77.9 per cent of Italian cases and a 32.81 per cent drop in cases from Iran.

Dr Grenfell said there were many different factors that went into the virus modelling.

"There were different variables like the infection rate in the source country and the length of the plane's flight and the length of the stopover," he said.

"What it does do is identify flight routes that are of greater risk and the people they carry on board."

The modelling was conducted using data from the original strain of Covid, and not the more infectious Delta strain that is crippling parts of eastern Australia.

A date has not been set for when international travel will be back on the cards for most Australians and when people can fly into Australia without being subjected to international travel caps.

Dr Grenfell said the modelling could help to provide governments with tools to help make a more educated decision as to when the international borders could reopen again.

"It could help to provide effective ways to show which flights could come through and could also be used to protect from the multitude of virus arrivals in the country," he said.

"It can be used to assist in the reopening process."

The findings were published in BMC Public Health.

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