As long as Australia opted for suppression over elimination, there would continue to be more waves until an effective vaccine was available.

"By that I mean no obvious community transmission - so people can basically return to semi-normal existence and businesses can mostly re-open," the HMRI epidemiologist and neurogastroenterologist said.

Professor Talley, the editor of the Medical Journal of Australia, said if we managed to eliminate community transmission, the restrictions in place - particularly in Victoria and NSW - would not be necessary.

"My argument is if we fail to do this, if we allow continued community transmission, the absolute guarantee is we will have more waves until we get a vaccine," he said. "That's the rationale, and I think it is do-able because it has already happened in parts of the country.

"In New Zealand it did happen until recently - there is a risk of further "contamination", but that's always the risk. We were close, and we are still close."

Professor Talley said the public health efforts in NSW had been "pretty successful".

"We are in the single digits," he said. "But the trouble is there is still community transmission.

"So we have got to get, in my view, that under control. We shouldn't let it bubble on and on and on, because the risk is, at some point, there will be a super-spreading event and we'll then have a major problem, and we don't want that."

Professor Talley said in hot spot areas such as Sydney, mask-wearing should be "compulsory" on public transport and in any indoor venues, and gatherings capped at about 20 people.

"Social distancing needs to be reasonably enforced in these areas, and pubs, clubs, and restaurants are high risk areas - they probably shouldn't be happening until we have no community transmissions.

"In doing that, with the public health efforts to test, trace and isolate, it wouldn't take too long to bring it totally under control and then you can then relax restrictions again while still paying pretty close attention."

Professor Talley understood businesses would be concerned about a reduction in activity, but argued if there was a major outbreak, businesses would be "very badly burned".

"There's this sense we can get it under control with aggressive contact teaching - which is possible, I suppose, but we haven't done it yet," he said. "We thought we had eliminated it from the community and everyone was very relaxed - it was a false security. In a pandemic you can't let your guard down, even a little bit."

Professor Talley thinks we are "about halfway" through the crisis now.

"In six months, a bit longer, we may well have a vaccine," he said. "Even if that is not fully effective, if it's partially effective and safe, then that will completely transform the whole situation.

"Based on what we know now, I am more optimistic than I have been."

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