From the difference between quarantine and isolation and how long patients are infectious: Everything you need to know about the Covid pandemic

Victoria's Chief Health Officer has attempted to clear up mounting confusion about the two main public health practices used to fight coronavirus.

Brett Sutton explained explained in a series of tweets on Sunday night the difference between quarantine and isolation and their role in fighting the pandemic.

He said the mandatory two-week quarantine is used as a precautionary measure to ensure a person who may have been exposed is not incubating the illness. 

Pictured: Victorian Chief Health Officer Brett Sutton addresses the media during a press conference in Melbourne in December

In a series of tweets, Mr Sutton explained that a mandatory two-week quarantine period is used as a precautionary measure

'Quarantine is 14 days (regardless of test results) because someone in quarantine could become positive at any point in this time frame,' he wrote.

'A negative test is no guarantee that you won't become positive later in the 14-day period. You may. You may not.'

He said isolation is required for confirmed cases to ensure they do not pass the infection on to others. 

'People with Covid-19 are understood to be infectious from one to two days before symptoms until a maximum of 10 days after, if symptoms have resolved,' he wrote.

Mr Sutton said people who are in hospital or have compromised immune systems are potentially infectious for longer and need to be in isolation for a lengthened period of time.  

'The main criterion to clear these people is that they are free of symptoms. A negative test also helps those with persistent symptoms,' the health officer wrote.

Pictured: Healthcare workers are seen attending to people at a drive-through Covid-19 testing facility at the Royal Melbourne Showgrounds in Melbourne on January 4

Pictured: a family at baggage collection area after arriving on Qantas flight from Brisbane at Tullamarine Airport in Melbourne on January 8

But he also explained why a negative test is not always required in order for someone to be released from isolation.

For people with weakened immune systems, 'the test can remain positive for days, or weeks, or sometimes months.

'That means the virus is detectable but it doesn't mean the individual is infectious. They almost certainly aren't.' 

The doctor explained that health officials are taking a 'cautionary' approach to the new strains of Covid-19, including the B117 mutation causing chaos in the UK. 

The variant of the virus has a mutated 'spike' protein on the outside which makes it better at invading the body, drastically increasing transmission rates.

While 70 per cent more infectious, B117 does not appear to be more severe in its effects.

The mutation has changed Australia's quarantine protocols after a woman with the UK variant flew to Brisbane from Melbourne after clearing quarantine on January 5.

Under the former protocols, the woman did not need to test negative to the virus before she was allowed to leave hotel quarantine after 10 days.

Until the new strain emerged, people who tested positive while in hotel quarantine were able to leave once they showed no symptoms for three days and 10 days had passed since they tested positive. 

Mr Sutton said that Australians with the new strain will have to isolate for 14 days from the onset of symptoms until experts have a clearer idea of how the mutation works.

Pictured: Digital signs encourage customers to wear face masks at Westfield Bondi Junction in Sydney's east

'Until it's clearer, we're going to be ultra-cautious and require the 14 days isolation,' he said. 

Patients will be tested at the end of the isolation period to help determine the risk based on the number of virus particles still inside the body, known as the viral load.  

A study by Public Health England and Birmingham University found the new variant 'had seen increase in relative viral load of between 10 and 1,000-fold' compared with samples of the original virus.

Victoria has recorded zero new locally-acquired coronavirus cases for a fifth consecutive day.

Just one new case was recorded on Monday, which was a returned traveller in hotel quarantine.

About 18,660 tests were conducted across the state in the past 24 hours. Victoria has 40 active cases, down from 45 on Sunday.