The Department of Health on Wednesday afternoon said it was investigating a confirmed case and would provide more information shortly.

Earlier in the day, authorities had warned Victorians will not get an early rules reprieve despite the state notching its first COVID-19 clean sheet since the fifth lockdown.

COVID-19 commander Jeroen Weimar said it was cause for quiet celebration and satisfaction.

"It's a symbolic marking of a point where there's no more COVID cases," he told reporters.

"It means we're on track with the strategy that we set three or four weeks ago."

But it has not inspired health officials to bring forward a review on restrictions and the current batch will remain in place until August 10.

"We still have active cases in our community right here that we know about ... we've still got just under 3000 primary close contacts ... and we still have ongoing risks in the rest of the eastern seaboard," he said.

He noted it was only a week ago that officials were caught off guard by the unlinked case of a Moonee Valley testing site traffic controller.

It remains unclear how the man caught the virus, but Mr Weimar said a review into the source of his infection would ramp up on Wednesday afternoon.

"There's a strong line of investigation around some movements that he had at work," he said.

Premier Daniel Andrews similarly cited Sydney's Delta outbreak as a reason for the state to take "cautious steps" towards greater freedoms.

"I fully acknowledge that there are some rules that are on at the moment that are very difficult, but they are nothing compared to being locked down again," he said outside parliament.

Opposition Leader Michael O'Brien, however, seized on the figures to call for the ban on home visits to be lifted and the 25 per cent cap on workers in offices to be increased.

"Our city is a ghost town," he said.

Active cases are continuing to fall, down from 124 on Tuesday to 99. As is the number of exposure sites, dropping to 33 after soaring to over 400 at the peak of the outbreak.

More than 30,000 test results were received over the past 24 hours, while about 17,600 vaccine doses were administered at state-run sites.

There are nearly 60,000 vaccination bookings available in Victoria, including some 14,000 Pfizer appointments each week until early September after second dose wait times at state clinics were upped from three to six weeks.

Naomi Bromley, deputy secretary of COVID-19 vaccinations, also said the health department was looking at rolling out AstraZeneca shots at mass vaccination hubs for Australians under 60.

"We are actively considering that at the moment, and we think we'll have more to say on that in coming weeks," she said.

None of the nine COVID-19 patients hospitalised in Victoria were fully vaccinated. Two remain in intensive care, including one on a ventilator.

Meanwhile, the Victorian-NSW border bubble officially tightened for residents just before midnight on Wednesday, with all non-essential movement across state lines outlawed.

Australian Associated Press