This includes 24 children aged 0-9, 39 aged 10-19, and 33 aged 20-29.

The youngest case was an 11-month-old baby.

Dr David Durrheim, of Hunter New England Health, said the amount of young people infected was "extraordinary and quite different to our first experience with the original Wuhan strain of the coronavirus".

"This has really taken hold in young people. We had one young fellow in his 20s, who needed a huge amount of oxygen support," Dr Durrheim said.

"Fortunately the team at John Hunter were able to keep him from having to be admitted to intensive care, but we were really worried about his health.

"He's now stabilised, which is great news."

Only four of 168 cases in this outbreak in the Hunter had unknown sources.

There have been 52 hospital admissions, including six children. No cases have been admitted to intensive care. Some patients are receiving care through the Hospital in the Home program.

Two deaths have been attributed to COVID-19. One was 85-year-old Bill Beecham, a resident at Hawkins Masonic Village in Edgeworth. He refused oxygen treatment in hospital. His wife Delma died in late June.

The other death was a returned overseas traveller.

Another resident in the Edgeworth village cluster died. His name was Kelvin Knight. He was 96 and in palliative care. He died with COVID not necessarily because of COVID.

Twenty-two people over 70 have contracted the virus in the region in this wave, but only one person in their 60s.

Cases among the older groups were mostly linked to the aged-care outbreaks at Edgeworth and Jesmond.

Dr Durrheim said the younger cases were partly due to behaviour, such as the gatherings at Blacksmiths Beach and a Shortland house.

There was also a cluster at International House at the University of Newcastle.

But he said the nature of the infections across age groups was "quite different".

"We saw the burden falling on older people in that first wave. We're now seeing the burden falling on young people," he said.

The virus had also spread in young families.

"There was the outbreak at Maitland Christian School. Some of the younger cases are linked there.

"We've also seen young children affected in younger family groups."

NSW Deputy Premier John Barilaro has remarked on the Hunter's impressive result, in reducing cases of the highly infectious Delta strain from a high of 24 cases to zero on Thursday. There were two cases on Friday.

"My team is pretty amazing. We have a highly skilled team with very good epidemiologists," Dr Durrheim said.

"We've got fantastic contact tracers who do very good interviews. Some of these people have gone back to do interviews up to four times to get the full story as it emerged and people improved recollections.

"Some of the groups have been very difficult to get an initial trust built up, so you have to go back."

He said "hard work, good fortune and divine providence" had played roles so far in this outbreak.

"It helps us to know where the virus is, to try and get ahead of the virus and it's certainly not been without its challenges," he said.

The public was also playing an important role.

"I think generally the public is doing the right thing. That's giving the virus less opportunity to spread," he said.

"In the first week before there was any real lockdown of movement - that was really challenging. We were behind the virus and it took a huge effort to catch up with it."

Public health measures had helped and people's compliance was critical.

"Less movement means the virus has less opportunity to spread," he said.

Honesty among affected people gives the contact tracers the chance to link close contacts and make sure they're isolated to help stop the virus spreading.

"The big challenge is this continual leak of COVID-19 from Sydney into the region," he said.

"We just need one of those introductions to go very badly wrong and we'll be behind the virus again and chasing it."

The highly infectious nature of the Delta strain has led to calls for children to be vaccinated.

There had been crippling outbreaks of Delta in schools overseas, according to Professor Raina MacIntyre of the Kirby Institute.

Additionally, new data showed "kids 0-3 years old transmit to adults more than older children".

"Ultimately, vaccination of children will be required to fully control SARS-CoV-2 [the virus that causes COVID-19], or it will become a pandemic of the young, with unknown long-term, generational health effects for our children," Professor MacIntyre wrote in The Conversation this week.

She said there was no safe "living with COVID" until at least 80 per cent of the "whole population" was vaccinated, including boosters or updated vaccines to tackle the Delta variant.

This was a much higher rate than 80 per cent of the "adult population", which Prime Minister Scott Morrison and Premier Gladys Berejiklian touted as a target to ease restrictions. This was equivalent to only 64 per cent of the total population.

Federal Health Minister Greg Hunt said on Friday that Australia's immunisation expert panel had approved the Pfizer vaccine for 12-15 year olds, which they could access from September 13. The Moderna vaccine is also being considered for this age group.

"Overall hospitalisation rates for COVID-19 in the adolescent age group are higher than for other diseases such as influenza," an ATAGI [Australian Technical Advisory Group on Immunisation] statement said.

"In the US, COVID-19 hospitalisation rates in adolescents from October 2020 to April 2021 were 2.5 to 3 times higher than that for influenza-associated hospitalisation rates from three recent influenza seasons."

Dr Durrheim noted that the virus had surged again in Israel, where 60 per cent of the whole population had been vaccinated.

"There were two groups in Israel that have allowed the virus to take off again. One was ultra orthodox members of the community and then children," he said.

"The virus took off in Israeli schools and has put a lot of pressure on the immunity in the community to the point that they've now introduced a booster dose of Pfizer vaccine.

"So we have a highly effective vaccine but, with that enormous source of infection in the community, they've had to introduce a booster dose to boost immunity."

Dr Durrheim said the key issue was to have "as high a proportion of the community vaccinated as possible" to keep people safe.

"We really need as many of us as possible vaccinated because this Delta strain, as we've seen in places like the US, has become a pandemic of the unvaccinated.

"People who are unvaccinated are ending up in ICU and dying. That's a grim reality."

Premier Berejiklian has talked repeatedly about living with the virus. Dr Durrheim believes some public health measures will need to be retained with this.

"But at some point, people who are unvaccinated are going to be incredibly vulnerable," he said.

Eminent immunologist Professor Peter Doherty said this week that children aged five and under will have to be vaccinated if Australia is going to defeat the Delta variant.

Professor Doherty said the infectiousness of the Delta variant, particularly among children, meant it would no longer be sufficient to only vaccinate children over 12.

"I think we should be going ahead with vaccinating down to age 12 as soon as we get enough surplus vaccine, but by October we should have the safety data on vaccinating down to age five and certainly even younger by the end of the year," he said.

Clinical trials with Pfizer and Moderna vaccines for young children began in the US in March.

Pfizer plans to release the data about its vaccine's efficacy among kids aged five to 11 by the end of September.

"If all goes well with FDA approval, we should see US kids under 12 being vaccinated from the end of 2021. They're already vaccinating down to age 12," he said.

Australia is also considering whether to vaccinate under 12s.

"If ATAGI approves the vaccine in the under 12s, I'd be encouraging everybody to have their kids vaccinated, but to get vaccinated themselves as well," Dr Durrheim said. "We want the regulator to carefully review the safety and effectiveness data. That has happened in the US and it looks very pleasing."

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