Things are going in the right direction in Victoria, its chief health officer, professor Brett Sutton said.

"[Case numbers have] not gotten below 100 yet, I do expect that to happen, if not over the weekend, by next week if trends continue," Prof Sutton said.

Thursday and Friday both saw case numbers increase by 113 people, the lowest number of new cases in eight weeks.

Premier Daniel Andrews said discussions about the stage four restrictions would happen once the state fell to double digits in new daily cases.

The death toll in Victoria is still high. The deadliest day this week was Wednesday with 24 deaths. The total death toll from COVID-19 in the state is 497.

Meanwhile, the Victorian government has pushed to amend the Public Health and Wellbeing Act 2008 in order to extend the state of emergency for a further 12 months, creating a cap of 18 months.

Victoria declared a state of emergency on March 16 this year and since then every four weeks that state of emergency needs to be reviewed. On September 13, this will mark six months of a state of emergency, and this is the maximum length for a state of emergency under the current laws.

After six months under the state of emergency, the government is required to seek approval for extensions from the state parliament.

"This is very much like an insurance policy. We certainly hope that we don't have to draw down on it," Mr Andrews said on Tuesday.

A state of emergency allows the Victorian government to make extraordinary laws, such as the curfews and laws on movement during stage four.

Victorian opposition leader Michael O'Brien described the proposal as "unprecedented, extraordinarily overreaching and anti-democratic" on Wednesday.

Mr Andrews said he was very hopeful about discussions with the Victorian crossbench on this proposal.

Residents of Victorian towns near the South Australian border have rejoiced as the South Australian government has loosened its borders.

There is now a 40-kilometre buffer zone between the South Australia-Victoria border was announced on Tuesday and put into effect on Friday.

The new buffer zone allows Victorian residents in border towns to go to SA for work, medical appointments, schooling and shopping.

"As of Friday, school students will be able to return to school in South Australia. Businesses will be able to resume as they were," South Australian Premier Steven Marshall said.

"There is one caveat on this and that is that we don't have further community transmission in that western part of Victoria between now and [then]."

More restrictions have loosened in South Australia. Since Friday, South Australians can have gatherings of up to 50 people at home.

Tasmanians, Western Australians, Queenslanders and Territorians who had to stop over at Canberra or Sydney airports would not need to isolate for 14 days, despite restrictions remaining for NSW and ACT residents.

"We are going to continue to look at this closely. If we continue to see low levels it is quite possible that we will remove the requirement for 14 days' isolation in the next two weeks," Mr Marshall said.

Schoolies has been banned in the Gold Coast after an increase in active cases in Queensland.

On Friday Queensland Premier Anastasia Palaszczuk announced three new cases of COVID-19 were found, bringing the state total to 20.

Those cases were all in their 30s, had only mild symptoms of infection and were connected to the corrections academy at Wacol, in Brisbane's western suburbs.

Two of the new cases lived on the Gold Coast, which has led to tighter restrictions in greater Brisbane, to be extended to the Gold Coast from Saturday morning.

"Coming into effect from 8am Saturday, we are going to extend those limits of people inside your homes to 10 people, and those gatherings outside to 10," Ms Palaszczuk said.

Queensland's chief health officer Jeanette Young expressed sadness for school-leavers after the cancellation.

"They've had a really difficult year. This is a rite of passage. Your last year of school is such an important year to get you prepared for going out and joining adulthood," she said.

The first phase of a vaccine trial is pre-clinical. Before scientists can test vaccines on humans there must be a robust body of data from laboratories, including animal studies. An independent ethics committee must be confident the potential vaccine is safe and effective to trial. If that is the case the vaccine moves to phase one.

Phase one trials are small with about 100 healthy volunteers participating. The main objective of this trial is to confirm the vaccine is safe. Blood tests are taken from volunteers to test the efficacy of the vaccine in the laboratory. Blood testing can indicate if the vaccine has created an immune response.

Phase two studies are larger with 1000-2000 volunteers, still broadly focused on safety but there is a greater focus on the efficacy. With volunteers, there may be a more diverse population to resemble the target population. Phase two trials are still too small to confirm if the vaccine does what it is supposed to do.

Phase three is where we find out if the vaccine works for its intended process and this is the pivotal phase before widespread use. This gathers data from tens of thousands of volunteers and the aim is to see if people who had the vaccine had significantly lower rates of infection.

Phase four refers to further trials of the efficacy of the vaccine once its use is widespread. Vaccines and the diseases they prevent are always evolving.