Future pandemic modelling in Australia to factor in increased severity of Covid Delta variant

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Future pandemic modelling conducted in Australia will take into account the Delta variant of Covid being more severe and deadly, epidemiologists say.

In a briefing on the Doherty Institute modelling that informs the national reopening plan, researchers said on Monday that evidence pointing to Delta’s increased severity has emerged since the initial modelling was conducted.

Prof James McCaw, from the University of Melbourne, worked with the Doherty Institute on the modelling and said when it was first conducted it was clear Delta spread more quickly, but it was less clear at the time whether infections caused more severe disease.

“Evidence that Delta was more severe in terms of clinical outcomes was either scant or certainly unsettled in the international community,” he said.

Related: ‘We are absolutely in crisis’: Sydney’s health workers on whether the system is coping under Covid | Joseph Freeman and Alexandra Martiniuk

Since then, two different studies have found patients infected with Delta are more likely to be hospitalised than patients infected with Alpha or the original virus. One of the studies, from Scotland, was published in June, while the other from the University of Toronto, in Canada, was published in August.

“Of course, as scientists, we update our understanding based on available evidence and it’s now far more clear that Delta is more severe,” McCaw said. “And so work and, say, forecasts … of potential hospitalisations … would account for the increased severity of Delta.”

Victoria’s roadmap for reopening takes the overseas findings into account.

A professor of epidemiology at the University of Sydney, Alexandra Martiniuk, said both the Scottish and Canadian data were “based on robust health datasets, national and province-wide datasets respectively”.

“This provides strength to the studies’ findings,” she said.

“In science, we grow confident in the data illustrating the ‘truth’ when multiple studies show the same thing. It appears likely that Delta is causing more severe disease and likely the addition of just one or two more robust studies will give stronger confidence in knowing whether this is true or not.

“Models simulate a range of scenarios to assist with decision-making and certainly models should consider the possibility that Delta is more severe. If we are using modelling to inform planning for loosening restrictions and for anticipating burden on our health system, then it does matter that our models take into account Delta’s increased infectiousness as well as its increased ability to cause more severe disease.”

Unvaccinated people remain the greatest concern, the studies show. The University of Toronto study found “a marked reduction in risk of severe disease and death among both partially and fully vaccinated individuals in our study”.

“Canada is now one of the most widely vaccinated countries in the world with respect to SARS-CoV-2 [Covid-19] and vaccination has undoubtedly blunted the impact of the emergence of these VOCs [variants of concern],” the study found.

Martiniuk said while the inputs into modelling for reopening Australia changed as new evidence emerged, most advice landed in the same place, finding a high level of vaccination combined with ongoing public health measures were needed.

Related: Why is Australia at odds over the Doherty report and what does it say about opening up the country?

New modelling from the University of Melbourne released on Tuesday supports a key finding in the Doherty report for reopening that keeping “light restrictions” as a minimum at all times will “dramatically” reduce the need for lockdowns.

It calls for the country to aim for a 90% vaccination rate among the adult population, saying this would slash hospitalisation and death rates by about 80%, and most likely mean no time in lockdown.

The University of Melbourne report, led by Prof Tony Blakely, says booster vaccines will soon be needed to address waning vaccine immunity for both AstraZeneca and Pfizer against the Delta virus. It calls for vaccinating the global population as a priority.

“This is important for equity and also because it reduces the chance of dangerous new variants emerging.”

The latest update to the Doherty modelling was released last week.

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