If Australia’s international border is reopened as highly transmissible variants of Covid-19 circulate abroad or locally, large and disruptive outbreaks will still be possible after 80% of people aged 16 are fully vaccinated, modeling released on Monday in the Medical Journal of Australia. said.

It comes after New South Wales Prime Minister Dominic Perrottet announced on Friday that from November 1, Australians and returning tourists could travel to Sydney without needing to quarantine at the ‘hotel. However, later on Friday Prime Minister Scott Morrison said the international border would only open to vaccinated Australian citizens and their immediate families and not tourists, saying “we will not rush.”

The modeling, led by Dr Mark Hanly of the Center for Big Data Research in Health at the University of NSW, applied various assumptions regarding transmissibility, the speed of vaccine deployment and the extent of border reopening to see the impact on virus cases and hospitalizations.

For scenarios that assumed a variant similar in infectivity to the Alpha variant, the opening of international borders was followed by an increase in local transmission if local restrictions were limited to mask wearing and social distancing. . However, “the number of people hospitalized with severe Covid-19 was very low” in this scenario, wrote Hanly and his co-authors.

However, if the variant to enter Australia had similar infectivity to the Delta variant and circulated when 80% of people aged 16 and over were fully vaccinated (64% of the total Australian population), the opening of the international border was followed by an increase in infections and hospitalizations. Modeling revealed that this was the case, whether 2,500 or up to 13,000 international arrivals were accepted per day. These surges would require public health measures beyond mask wearing and social distancing to avoid overwhelming the health system, according to the modeling.

“The planned reopening of Australia’s borders to international travelers increases the risk of introducing new chains of infection and new variants of SARS-CoV-2,” the modeling revealed.

“Policymakers and health systems should not focus exclusively on defining immunization thresholds at which particular restrictions could be removed. Instead, they should recognize that mass vaccination is unlikely to provide complete protection against Covid-19. “

Melbourne’s Deakin University Chair of Epidemiology, Professor Catherine Bennett, said it was important to note that the modeling did not assume any viruses in the Australian community as a benchmark when variants came from overseas.

“So that’s no longer true,” Bennett said. “We already have restrictions in place, which we are going to yes, we are going to relax, but we are not going to get rid of them completely.”

The model also assumed that additional public health measures beyond mask wearing and social distancing, such as school closures, would not be introduced until new cases hit 10,000 per day. Bennett said it was likely that additional restrictions would be triggered much sooner than the model assumed.

“It is likely that measures would be implemented that would prevent us from reaching 10,000 cases,” Bennett said. “This modeling emphasizes that the focus should actually be on the kinds of health and safety measures that lead to prevention, rather than waiting for the virus to slip away before introducing them. And the good news is that I think the proposed international reopening falls within these parameters of prevention. “

However, Professor Mary-Louise McLaws, an infection control expert from UNSW and a member of the World Health Organization’s Covid Advisory Board, said she was concerned about the reopening of New Zealand’s international border. -South Wales announced by Perrottet.

McLaws said while she was comfortable with the removal of the hotel quarantine, it would be important to test returning Australians for the virus the day they boarded the plane, upon landing. , and to send home only those who have tested negative. Those who tested negative should still be tested with a rapid antigen test every day for five days, she said, and again five days after that.

“That way you then run a tiny risk of being a source of infection for unvaccinated and immunocompromised people,” she said. “Even people who are fully vaccinated are at risk of carrying the virus. “