The interval between doses of the AstraZeneca COVID-19 vaccine has been halved to six weeks in Victoria, in a push to ramp up inoculation rates and curb virus transmission.
Acting Chief Health Officer Ben Cowie announced the change on Thursday, as the state recorded 176 new COVID-19 cases - its highest daily figure since August 22 last year, when 202 infections were recorded.
"If you're sitting at seven weeks, eight weeks, nine weeks (between doses), go and get your double dose now," he said.
Professor Cowie said the change, effective immediately, as well as additional supplies of the Pfizer vaccine from the Commonwealth government, would help the state reach its immunisation targets faster.
There is about 52,000 appointments available at state-run vaccination hubs in the coming weeks.
"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," he said.
The wait time between AstraZeneca doses is now the same as for Pfizer, which was extended from three to six weeks due to limited supply.
The Australian advisory group on vaccinations recommended a shorter interval of four to eight weeks between AstraZeneca doses in outbreak settings, as COVID-19 cases in NSW began steadily rising in mid-July.
Clinical trials, however, have shown the vaccine is most effective with a dosing interval of 12 weeks.
Prof Cowie said the state had to strike a balance between long-term vaccine efficacy and getting the highest level of protection against the Delta variant.
He said two doses of the AstraZeneca vaccine reduced the risk of infection by 70 per cent and the risk of hospitalisation by 90 per cent.
Victorians aged 18 to 39 can book to get the vaccine at a state hub, GP or pharmacy, though they will need to provide informed consent due to the increased risk of a rare clotting disorder.
Of the state's 176 new cases, 83 are linked to known outbreaks, with the source of the remaining 93 infections under investigation.
Authorities did not provide information on how many cases were self-isolating during their infectious period.
Sixty-seven cases are located 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 case in Geelong.
"There's not one corner of metropolitan Melbourne that's not touched by this virus," Prof Cowie said.
Health Minister Martin Foley said an outbreak at a Melbourne call centre is of particular concern to authorities, as the office space is shared with Healthcare Australia. It provides workers for the state's vaccination hub.
Seventeen people who work at the call centre have tested positive and 400 primary close contacts are now self-isolating.
Mr Foley said a public health response was also underway at Base Backpackers in St Kilda, where a case was residing before they tested positive. They have since been moved into hotel quarantine.
The government has conceded efforts to bring cases down to zero have failed, with tough restrictions to stay until at least 70 per cent of eligible Victorians are fully vaccinated.
Some reprieve will be granted when 70 per cent have received their first vaccine dose, which was forecast on Wednesday to happen about September 23 - that time has now shrunk to September 19.
Of the state's 1029 active cases, 61 are in hospital, including 20 in intensive care, with 13 on a ventilator to breathe.