Health authorities are now vexed over their next moves.

As Chief Minister Andrew Barr pointed out on Friday, the ACT - like all jurisdictions - had done the "hard yards" against the Delta variant and the Canberra community, in particular, has responded magnificently to the vaccine call.

But just as we were peeling back our masks and preparing for a little Christmas cheer, in marches the most contagious COVID variant yet.

The ACT has moved quickly to impose 14-day quarantine requirements for close contacts of its Omicron cases, as well as their household contacts - regardless of the individuals' vaccination status.

MORE COVID-19 NEWS:

There are 20 close contacts associated with the confirmed case, and a further 33 returned travellers on the same flight have also been deemed close contacts.

With Queensland and WA still sealed off until mid-December, South Australia Premier Steven Marshall appears the most jittery of the recent re-openers.

It's the risk of the unknown that has everyone in a lather.

South Australia's chief health officer, the highly respected Professor Nicole Spurrier, said her health team was particularly concerned about vaccine efficacy against the new strain, the severity of the variant, and high rates of reinfection observed abroad.

The latest data suggests Omicron can infect three to six times as many people as Delta, over the same time period.

The variant's swift rise in South Africa also hints it has some capacity - although that's still being assessed - to evade immunity.

So here's the huge conundrum faced by our health experts as we lead into a much-needed - economically and socially - Christmas holiday period.

Should the states and territories, all having done the Delta "hard yards", jump as quickly as before on closing things down and keeping people home?

The early read on this is that very few premiers and chief ministers have the appetite for it.

They will hold off for as long as possible while scientific data is closely examined from around the world, desperately hoping for news this new threat is manageable.

The worst possible outcome would be that Omicron has the capacity to evade vaccine immunity.

Vaccination has been championed as our silver bullet solution.

Without that assurance, the future looks highly uncertain.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: