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Millions of Australians could become infected and tens of thousands hospitalised with COVID-19 if we reopened Australia and let the virus run wild with 70% of the population vaccinated.

The national cabinet plan, released on Friday, would have Australia slowly reopen once 70% of over-16s are vaccinated. That’s 56% of the population. With no extra measures such as mask-wearing and social distancing, modelling by mathematician and Monash university adjunct professor Michael Georgeff shows cases would increase to 5 million and 27,000 deaths over time if the population received only the AstraZeneca vaccine. Other models show similar surges. Even with extra precautions, case numbers would reach massive peaks.

But high cases are something the vaccinated world will have to get used to. Instead it will have to focus on hospitalisations and case severity as a marker for success. 

Unfortunately, the Delta strain has shown that even among vaccinated individuals, the likelihood of developing serious illness is higher than other strains, meaning Australia will have to look abroad and move slowly and carefully as it tries to return to normality. 

What does the modelling say? 

Georgeff’s modelling shows that with 56% of the population vaccinated with AstraZeneca, combined with precautionary measures, total infections would eventually reach 3.8 million, with 45,000 hospitalisations. This drops to 1.8 million and 300,000 for those vaccinated with Pfizer. 

The modelling uses the reproductive value of the Delta strain, where each infected person will infect another five on average (although many models show it could be as high as six), combined with the efficacy of masks and social distancing which is expected to reduce transmission by 35%. 

Similarly, modelling led by James Cook University shows that with no restrictions and a population where half the vaccinated people received AstraZeneca and the other half Pfizer, about one in three people would eventually become infected, with about 100 fatalities in every 100,000 people. The Grattan Institute has slightly different figures that show almost 27,000 peak daily cases and 15,900 deaths with 70% vaccination coverage involving limited precautions.

Accenture research, which Crikey has not seen, shows similar numbers. If 70% of the population was vaccinated, Australia could tolerate up to 10,000 new cases and fewer than 20 deaths a day. 

Restrictions are here to stay

Head of the epidemiological modelling unit at Monash University James Trauer, who worked on the James Cook University research, tells Crikey the data showed herd immunity was likely to be off the cards.

“We will have large numbers of cases as we shift out of this elimination approach,” he said. 

“When we get to that point, we should be looking less at case numbers and more at hospitalisations and deaths and the burden on the health system, but we are likely to have a large epidemic at that stage.”

This is exactly what other countries are experiencing. The UK is recording more than 1000 new cases a day and dozens of deaths, even with over 70% of the adult population vaccinated. Unlike Australia, much of the UK population has caught and recovered from COVID, giving them some natural immunity — although how long it lasts is unclear. 

Georgeff says the data shows the importance of maintaining social distancing and mask-wearing: “Unless we get up to the 90% to 95% vaccinated level, we’re going to be wearing masks forever.

“We have to start accepting the fact that we will get 10,000 to 20,000 infections a day and just say, well, that’s going to be normal, as long as enough people are vaccinated.” 

Precautions will be key to flattening that curve to ensure hospitals aren’t overwhelmed, he says. 

Slow and steady wins the race

Walter and Eliza Hall Institute epidemiologist Professor Ivo Mueller is a little more optimistic: “I don’t think that you will see cases in hospital skyrocket because [the national cabinet’s plan] is a very gentle, very careful reopening.”

This is different from the UK where Prime Minister Boris Johnson ended laws mandating the wearing of masks and the enforcement of social distancing on July 20 in what was known as “Freedom Day”. 

“It puts us in a completely unique position in the world because elsewhere in Europe or the US they’re reopening from the background of having had a huge catastrophe,” Mueller said.

“There, people are trading off a certain risk for more freedoms, whereas we have to trade off a certain increase in rates of freedom on the background of having had very little risk, and the suggested pathway forward is very carefully trying to manage that.”