Ms Stephen-Smith said the government was aware for some time about the gathering at a Wanniassa residence on Saturday, October 30.

"We don't generally talk about those transmission events when they occur at private events, and they're not a public notification," she said.

"Given that it's not a public site, it's not a public exposure risk."

The Health Minister said these events were investigated where appropriate by ACT Policing and that ACT Health worked directly with people for contact tracing.

University of South Australia biostatistics expert Adrian Esterman said individual "superspreaders" could turn one case at a party into many cases.

"You could have a big party, and no one's infected there. You could have a big house party, and five people are infected, but none of them are superspreaders.

"But it just takes one superspreader to be in that party and, whack, you get 30 cases."

Professor Esterman said most people infected with COVID-19 passed the virus on to two others or less but he warned of individual "superspreaders". These people accounted for roughly 10 per cent of COVID-19 cases but infected 80 per cent of all others.

With Australians preparing to travel over the Christmas period, Professor Esterman said similar clusters could emerge across the country.

But he said the ACT was bolstered by consistent vaccination compared to jurisdictions like Victoria, where coverage was high but patchy, and WA, where vaccination was still lagging behind.

"This is now going to be an epidemic of the unvaccinated," he said.

Professor Esterman said only three countries - Malta, Portugal, and Iceland - had comparable vaccination rates to the ACT, and warned they would not provide insight into how the virus will develop.

"I wouldn't say that ACT was comparable to those [countries] ... so the trouble at the moment is we're in unknown territory," he said.

"We simply don't have anywhere in the world where we can say: this is what's going to happen in the ACT."

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The Health Minister said the 33 cases associated with the cluster included secondary and tertiary transmission to people who were not present at the event.

When asked if ACT Health could be sure that all individuals at the party had been contacted, Ms Stephen-Smith said she thought most attendees would be aware if others had contracted COVID-19.

"I think the people who were at that event will know that other people at that event have been identified as COVID cases and they will know whether they've been there or not. If they want to contact ACT Health that would be great," she said.

"And ACT Health makes every effort as it does always with their contact tracing and case investigation to identify as many people as they can through contact tracing."

Ms Stephen-Smith suggested there was more than one event on the same night and that some people had confused anther private event with the party that had sparked the chain of transmission.

"It appears from what I'm hearing that there has been some confusion in the community and there have been some allegations that it was one event when it was actually a different event that we're talking about here. So I would really encourage people not to speculate about this event, not to make assumptions."

She said transmission had occurred at a number of private events over the past few weeks.

Since schools returned to face-to-face learning, there have been 17 exposure locations in Canberra schools but only two school sites had experienced transmission of the virus.

A cluster of cases associated with the Wanniassa School junior campus had reached 50 on Tuesday, including secondary and tertiary infections, while there were less than five cases linked to Erindale College.

Alfred Deakin High School was added to the list on Thursday, while Mawson Primary School was reported on Wednesday.

The ACT recorded nine COVID-19 cases in the 24 hours to 8pm on Wednesday.

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