The interval between doses of the AstraZeneca COVID-19 vaccine has been halved from 12 to six weeks in Victoria, as the state records 176 new infections.

Acting chief health officer Ben Cowie said the change would be reflected on the state’s vaccination booking website from Thursday.

“This change and the additional supply of Pfizer vaccine from the Commonwealth, when it arrives in Victoria, will help us to reach our vaccination targets faster,” he said.

“But more importantly, they will really contribute to the response to community transmission, put a downward pressure on cases, and contribute to protecting the health system.”

The change makes the wait time between AstraZeneca doses the same as for Pfizer, of which Victoria has limited supplies.

Victoria has set a target of “five million jabs in five weeks”, aiming to have 70 per cent of its eligible population with a first dose by mid-September. Tight restrictions will last, particularly for Melbourne, at least until then.

Professor Cowie said there were more than 52,000 available AstraZeneca appointments in coming weeks.

Of the state’s 176 new cases on Thursday, 83 were linked to known outbreaks, with the source of the remaining 93 under investigation.

Health Minister Martin Foley said 67 patients were in the northern suburbs of Melbourne, 61 in the west, 22 in the east and south, 13 in the regional town of Shepparton and one in Geelong.

“We know cases have emerged recently in the northern and western suburbs,” he said.

“We are also now starting to see more cases spring up into the eastern and southern suburbs of Melbourne.”

In recent days, there have been wastewater detections of the virus in Melbourne’s south, including Armadale, Prahran, South Yarra, Toorak, Windsor, Aspendale, Aspendale Gardens, Bonbeach, Chelsea and Chelsea Heights.

In the city’s south-east, there have been similar results for Burwood East, Forest Hill, Glen Waverley, Scoresby, Vermont South and Wheelers Hill.

It is not yet clear how many of Thursday’s cases had been in isolation while infectious.

Mr Foley said an outbreak at a Melbourne call centre for the state’s coronavirus hotline was of particular concern to authorities.

Some 17 people who work at the call centre have tested positive and 400 primary close contacts are self-isolating.

A case at Base Backpackers in St Kilda is also a concern. The person has been moved into hotel quarantine.

There are 1029 active cases in Victoria, including 61 battling COVID-19 in hospital.

Twenty are in intensive care, including 13 who are on a ventilator to breathe.

It is the state’s second consecutive day of more than locally acquired 100 cases, after 120 were reported on Wednesday.

The government has conceded efforts to bring cases down to zero have failed, with tough restrictions to remain in place until October.

Authorities have shifted their focus to suppressing the outbreak, keeping the health system from being overwhelmed, while racing to reach higher vaccination coverage.

Mr Foley said more than five million vaccines had been administered across Victoria, including 33,720 in state clinics on Wednesday.

-with AAP