Victoria has shortened the interval for COVID-19 vaccine booster doses in response to the Omicron surge which is overwhelming the state's health system.
Premier Daniel Andrews said it meant the total number of people who were eligible would now increase substantially by about 1.2 million.
The change, which will be in place at state-run hubs, is in line with earlier advice from Australia's vaccine advisory group ATAGI.
"It is safe, it is effective," Mr Andrews said.
"There are currently 1,365,004 Victorians who are 18 and over and have had a third dose," he said.
"And with the announcement I've just made, effective immediately, reducing the interval down to three months, there are now 2.45 million Victorians who are eligible, but have not yet had their third dose."
The change is consistent with rule changes in NSW and South Australia.
There will be a booster "blitz" of 60,000 shots on the weekend, with longer hours and walk-in allowed at some centres.
Department of Health deputy secretary Naomi Bromley said reducing the interval would mean that someone getting a booster shot this weekend would have full protection within the first week of February.
Monash Health's Rhonda Stuart said immunity after the second dose waned at the three-month mark.
"Which is why … that bringing forward that third dose to three months is going to make a big difference to the community," Dr Stuart said.
Dr Stuart said Omicron cases were filling the hospitals.
"We are seeing many patients hospitalised across services and we know that less than 5 per cent of them have had a booster dose," she said.
Third dose may become mandatory, Premier says
Mr Andrews said there was "every chance" the third dose would soon become mandatory to be considered fully vaccinated.
Currently, workers in key sectors who are already required to be fully vaccinated with two doses must get their third dose before being permitted to work on site.
This applies to healthcare, aged care, disability, emergency services, correctional facilities, quarantine accommodation and food processing and distribution workers, excluding retail.
"I have been clear with people that there is every chance that we add to that list," Mr Andrews said.
Victoria's COVID-19 hospitalisation rose to 1,173 on Wednesday, up from 1,152 reported on Tuesday.
A further 18 deaths were recorded in the state.
Of the patients in hospital, there are 125 in intensive care, 42 of whom are receiving ventilation.
There are now at least 253,827 active cases in the state.
The state has officially recorded 20,769 new COVID-19 infections, but the true number of new cases in the community could be much higher.
The new cases were reported from 10,726 PCR results and 10,043 at-home rapid antigen tests (RATs).
About 26 per cent of Victorian adults have received three doses of a vaccine so far.
There were 22,121 vaccine doses delivered on Tuesday at state sites, with 5,144 aged between five and 11.
Mr Andrews said 104,000 bookings were made in the last seven days. Of those, 68,000 were booster doses, and 33,000 the first doses for five-to-11-year-olds.
ADF personnel called in to help
Australian Defence Force personnel will help to ease the pressure on the struggling Victorian health system.
This comes as a statewide Code Brown alert came into effect at midday, allowing hospitals to redistribute staff and resources to respond to an influx of patients.
Mr Andrews said about 20 personnel would work with paramedics as "blended crew", with the paramedic providing the care, and the ADF member helping and driving.
"It just means many, many patients will get the care that they need as fast as possible."
Mr Andrews said Commonwealth public servants also continued to support the Victorian community, taking triple-0 calls to reduce pressure on the staff.
He said the arrangement was scheduled to end this month but was now an ongoing approach and Victoria would ask for more help if needed.
On Tuesday, the Victorian government drew flak for halting IVF treatments, along with other "non-urgent" elective surgeries. Women due to begin new IVF treatment cycles after January 6 having to wait until mid-April to resume.
Mr Andrews said he apologised for the impact the decision was having on people and working hard to get day procedures, including IVF, reinstated as soon as possible.
Mr Andrews said he was not trying to minimise the impact of the decision, but the most time-critical IVF procedures were still taking place.
"We understand this is distressing. We are doing everything we can to have the … same-day surgeries back on," he said.
More workers now exempt from isolation requirements
From Wednesday, more critical workers have joined workers in the food production sector as being eligible for exemption from quarantine as close contacts of people diagnosed with COVID-19.
Those in emergency services, education, critical utilities, custodial facilities, transport and freight may not have to quarantine for seven days, if they are asymptomatic, wear a mask and undertake daily testing.
The chief executive of Ritchie's IGA, Fred Harrison, said many businesses would not be able to facilitate the return of workers due to the cost of rapid antigen tests.
"It's going to be an astronomical cost; you're almost better off to say, 'have your seven days off, and then come back after your 7th day,'" he said.
Mr Harrison said the government would need to provide tests if the new rules were to improve supply chain issues and staff shortages.
Victoria Police confirmed it would not allow close contacts to return to work, due to a shortage of rapid antigen tests.
A spokeswoman said Victoria Police did not currently have enough tests to allow isolating employees to return to work.
It is hoped those supply issues will be resolved in coming weeks, she said.
