Several Metro Train services into Melbourne’s CBD have been added to the list of close to 400 coronavirus exposure sites in Victoria.

Six services on the Upfield Line between Merlynston and Flinders Street stations and Melbourne Central and Merlynston Station have been named as tier two sites.

Anyone who travelled on those lines at the specified times must quarantine until a negative result is returned.

The public health alert, issued by the Victorian Department of Health late on Sunday, affects passengers who travelled in and out of Melbourne’s CBD between last Wednesday and Friday.

The warning came after four new cases were reported earlier on Sunday, including two linked to the Arcare Maidstone aged-care home in the city’s north-west.

One is a 79-year-old resident who has had both doses of the Pfizer vaccine. They live close to two other residents, aged 99 and 89, who have previously tested positive.

The resident, who is asymptomatic, has been taken to hospital.

The other case is a registered nurse who worked at the nursing home on Saturday and has received her first COVID-19 shot.

Both are primary close contacts of previous cases, including a primary school teacher linked to the West Melbourne outbreak, which has infected 10 people with the Delta variant.

Tweet from @VicGovDH

Delta strain ‘more transmissible’

Victorian authorities are still on the search for the source of the state’s worrying Delta strain.

On Sunday, Britain’s Health Secretary Matt Hancock revealed the variant is 40 per cent more contagious than the Alpha strain that emerged in Britain.

“That figure, around 40 per cent more transmissible, is indeed the latest advice I have,” he told Sky News.

Mr Hancock said the Delta variant, first detected in India, had made the virus “more difficult to manage”.

But fully vaccinated people are protected, he said.

“After two doses of vaccine we are confident that you get the same protection that you did with the old variant,” Mr Hancock said.

“The good news is that the vaccine still works just as effectively. Everyone has to get the second dose because, with just the first dose, it’s not as effective.”

The Delta strain has been identified in 62 countries, according to the World Health Organisation’s latest epidemiological update.

“The majority of people going into hospital with COVID now are unvaccinated,” Mr Hancock said.

“But it’s good news for all of us because it shows that the vaccine protects you from going into hospital.”

A decision on Melbourne restrictions easing

Only 2-3 per cent of Victorians have so far been fully vaccinated as Melbourne emerges from its second weekend of lockdown.

Victoria’s deputy chief health officer, Allen Cheng, said it was difficult to say what proportion would need to be vaccinated to avoid future lockdowns.

“There isn’t one single magic number,” Professor Cheng said on Sunday.

“Once you get up to much higher coverage rates, then it makes a whole lot of things easier.

“We may not need the intensity of restrictions. We may be able to only do contact tracing without having to do other things quite to the same level, and that is the benefit of vaccination.”

Professor Cheng expects Melbourne’s restrictions will ease as planned on Friday.

“We don’t want to be in this any longer than we need to. So if we can, we will lift it early,” he said.

-with AAP