But Canberrans have been warned eligibility for Sotrovimab, designed to prevent mild COVID-19 progressing to severe disease, was strictly limited and the treatment was no substitute for vaccination.

The first patient in the ACT was treated with the drug this week, after it was granted provisional approval by the Therapeutic Goods Administration in August.

Infectious diseases physician at Canberra Health Services Nick Coatsworth described Sotrovimab as a "welcome addition" to the nation's fight against COVID-19, but warned its availability should not lead to complacency over vaccination.

"You've got to carefully select the patient who gets it. It's not for everybody and it's definitely not a substitute for a vaccine," he told The Canberra Times.

"Your own immune system recognising COVID because you've been vaccinated is by far and away the best defence.

"But once you have COVID, it doesn't matter what treatment we give you: you're still rolling a dice that it's better not to have to roll."

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Approval was limited to those aged over 55 with mild COVID-19 symptoms, who had received one or no vaccine dose.

Fully vaccinated people with conditions placing them a greater risk - diabetes, kidney disease, obesity, heart conditions - were also eligible.

International studies found the drug reduced the chance of long-term hospitalisation or death in those patients by 79 per cent.

The Department of Health predicted Sotrovimab would be recommended to between eight and 15 per cent of adults who contracted the virus.

The treatment needs to be given in hospital after being prescribed by a doctor. It's administered intravenously in a single dose, within five days of the onset of symptoms.

Australia secured an initial allocation of 7700 doses last month.

As Australia edged closer to the Doherty Institute's vaccination targets triggering the national reopening plan, attention has turned to intensive care capacity across the country.

Dr Coatsworth expected the drug to ease pressure on Australia's hospital system, but conceded to what extent it would reduce ICU admissions remained unclear.

"We don't know how much it'll prevent it ... everything we give people when they come into hospital and require oxygen is designed to stop them from going to ICU. This is just another addition to that," he said.

In May, the US Food and Drug Administration granted emergency approval for Sotrovimab in patients aged 12 or over, provided they were at "high risk for progression to severe COVID-19". It was also approved for that age range in the European Union.

The ACT was contributing to an Australian clinical program, and the the provisional use of Sotrovimab would continued to be monitored across the country.

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Dr Coatsworth said Sotrovimab would always be a greater benefit to people at high risk of severe symptoms. But he said it was too soon to tell whether it would be expanded to other cohorts.

"We should gather the Australian experience with the drug first. Then if we get supply and it proves to be beneficial in other groups, we can use it a bit more widely," he said.

"We don't know yet because we've only seen what's happened with it in the US studies."

Sotrovimab worked through laboratory-made proteins mimicking natural antibodies, already produced by the immune system to ward off illness.

It was the second COVID-19 treatment made available for use in Australia, after the TGA gave the green light to Remdesivir in July.

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