How Delta variant secretly spread inside a school and in families

See the full timeline of everything we know — and don’t — about how the latest quarantine leak spread throughout Melbourne.

Victorians thought they were dealing with just one outbreak until a few days ago, when we learned a variant — which authorities have now linked to a Melbourne quarantine hotel — had infected a West Melbourne family.

The outbreak has now grown to 15 cases and authorities are still trying to unravel the mystery of its source.

So how did it spread?

Genomic sequencing revealed on Tuesday, June 8 the variant behind the West Melbourne outbreak had been matched to a returned traveller who had stayed in Melbourne’s hotel quarantine system the previous month.

The man arrived in Australia from Sri Lanka on May 8, when he went into the state’s hotel quarantine system, and tested positive on arrival.

When his test result came back the next day, May 9, he was moved from the Novotel Ibis to the Holiday Inn health hotel.

He was released from quarantine on May 23 — after completing his 14 days and testing negative twice — has since been living in the city of Glen Eira.

Officials are still trying to figure out how case one — that is, the first person to test positive in the local outbreak — was infected, though they do have some theories about the quarantine leak.

Case one was tested on May 31 — several days after he and his family returned from a short trip to southern New South Wales.

Authorities announced his positive test on June 1 with cases two, three and four — the man’s spouse and two children — confirmed the following day.

Two youths walk past North Melbourne Primary School, where Covid was transmitted in a classroom. Picture: Tim Carrafa

CHO Brett Sutton told the press conference contact tracers hadn’t found any crossover between the family’s movements and exposure sites but alarm bells weren’t ringing — yet.

In addition to several NSW locations, North Melbourne Primary School — attended by the children — was declared a risk and eventually more than 240 tier one contacts were ordered into isolation.

A family connected to the school later tested positive, with a grade five student and classmate of one of the West Melbourne children confirmed as a positive case on June 4.

Two adults in their household, becoming cases five, six and seven.

The family’s other child, case eight, initially returned an indeterminate result before being added to the outbreak’s total.

But, as a result of the returned traveller link announced on June 8, authorities said they are now reconsidering their initial theory about the order of infections.

They said it was possible that the second family to test positive were actually the ones who passed the virus onto the family who travelled to Jervis Bay, but investigations are still continuing.

North Melbourne Primary School has been closed after Covid infections were linked to the site. Picture: NCA NewsWire / Andrew Henshaw

A work colleague of an adult from the original West Melbourne family, was also confirmed as a positive case on June 5.

The following day, the primary school was connected to another positive case, with the teacher of the two grade five students testing positive.

Their result brought the number of cases connected to the West Melbourne outbreak to 10.

Four new cases were announced on Monday, June 7, one of whom was a child of a previously announced case.

The three other cases are family members of a previously announced case.

Authorities did not say which previously announced cases the two groups of new cases were connected to.

On June 8 — the day a genomic match was found — another child connected to the outbreak was added to the case tally.

But while health officials have tracked how the virus spread from a family of four to a primary school and a workforce, authorities still don’t know how the West Melbourne family was infected.

HOW DOES DELTA COMPARE TO OTHER VARIANTS?

The Kappa and Delta strains are about 50 per cent more infectious than the Alpha variant. If someone with Covid-19 is in contact with 100 people, they will, on average, pass the virus to eight people for the Alpha variant, 11 for Kappa and 12 for Delta.

HOW DOES THE HOSPITAL ADMISSION RATE COMPARE?

Britain is reporting a 2.6-fold increase in hospital admissions with Delta compared with Alpha. However, this is based on small numbers so could change as researchers have more data. Importantly, 73 per cent of people admitted to hospital have not been vaccinated.

ARE THE VACCINES EFFECTIVE AGAINST IT?

The vaccines still offer protection against both the new variants, although it could be “slightly reduced” with the Delta and Kappa strains. Two doses of Pfizer provide 80 per cent protection against the Delta variant, while two doses of AstraZeneca provide about 60 per cent protection.

WHERE HAS IT COME FROM?

The source of Melbourne’s cases is not clear. Professor Sharon Lewin believes it’s likely to have been imported via a hotel quarantine breach, but it isn’t known whether it happened in Victoria or in another state or territory.

COULD IT HAVE COME THROUGH SOMEONE WHO HAS AN EXEMPTION FROM QUARANTINE?

It is possible but exemptions are rare.

ARE THE SYMPTOMS DIFFERENT?

Symptoms appear to be the same.

COULD THE SEQUENCING BE WRONG AND THERE IS NO DELTA HERE?

It’s not a lab error. Several cases have been sequenced.

Source: All information on the Delta variant is based on Doherty Institute Director Prof Sharon Lewin’s presentation at the June 5 state government Covid press conference.