Weighing the Omicron threat: how safe are you and your family as 2021 draws to an end?

Yet, as the explosion in case numbers in South Africa, the United Kingdom, the United States, Denmark plus others reveal, at least one thing is already beyond contention: the transmissibility of Omicron is astoundingly high.

So high, in fact, that it's clear it even outpaces that of the frighteningly contagious Delta variant. One need only cast their mind back to May this year to fully comprehend how alarming that is.

On the other hand, there is one important difference between the situation we confronted mid-year and that which we face now. Most of the population, at least in Victoria, is fully vaccinated.

Which is to raise the question: does full vaccination provide sufficient protection against the Omicron variant? Can we still enjoy a COVID-normal festive season as the curtain finally closes on 2021?

The early indications were positive. Doctors in South Africa, for instance, were reporting milder than expected symptoms in their Omicron-infected patients.

IN OTHER NEWS

But in some gloomy news for a beyond COVID-weary public, a growing body of evidence shows the Omicron variant to be skilled at reducing the effectiveness of both the Astra Zeneca and Pfizer vaccines.

Last week, the United Kingdom's leading epidemiologists released a joint study on the effectiveness of the COVID-19 vaccines against the Omicron variant.

The study showed that in a person who had been fully vaccinated with Astra Zeneca, Omicron reduced vaccine immunity to zero within 15 weeks of the person's second dose.

In other words, any person vaccinated with Astra Zeneca more than four months ago today has no protection against Omicron, at least when it comes to mild to moderate disease.

While the Pfizer vaccine fared slightly better, vaccine effectiveness against the Omicron variant was also shown to wane by around the four-month mark of a person's second dose. By that point, vaccine effectiveness drops to between 34 and 37 per cent.

By contrast, the Pfizer vaccine remains 64 per cent effective against the Delta variant more than six months after the second dose.

The only good news to emerge from the study was that a Pfizer booster shot was shown to increase vaccine effectiveness to over 70 per cent. And that applied whether a person's primary course was Astra Zeneca or Pfizer.

Burnet Institute epidemiologist Mike Toole said any person vaccinated with Astra Zeneca more than four months ago and who is yet to receive their booster shot was, according to the study, acutely vulnerable.

"The UK data shows that it's those people - predominantly people in the 60s age bracket - who have no protection against Omicron," Professor Toole said.

"If I were a person in that situation, I wouldn't be going anywhere near a restaurant today - you're a sitting duck."

Though the Delta variant remains the dominant variant of concern in Victoria, health authorities on Friday said they were managing 13 confirmed Omicron cases, with about 30 further cases being treated as suspected Omicron cases.

In the circumstances, Professor Toole said he wouldn't be surprised if ATAGI narrowed the recommended interval between the second dose and the booster to three months, as the United Kingdom had done.

"There's definitely a need to speed up the roll-out of the vaccine booster program because that will be the most effective way of preventing an increase in hospitalisations," he said.

But on Friday afternoon, the federal government said the five-month waiting period for a booster shot was to remain for the foreseeable future.

So, what does all this spell for your Christmas plans next week?

Professor Toole said that ideally everyone should get a rapid antigen test on Christmas Eve or the day before to reduce the risk of Omicron fuelling outbreaks similar to that currently playing out in New South Wales.

With a reproductive rate of more than two, Professor Toole said the surge in coronavirus infections in New South Wales would reach 25,000 per day "by the middle of January, not the end of January", as initially forecast by some.

"It's far too early to say Omicron does not result in severe disease," he said. "In the UK there's been a ten per cent increase in hospitalisations this week."

"But even if we could assume it was only half as severe as Delta - and there's nothing yet to suggest that - with huge numbers of infection, you'll end up with the same number of people in hospital.

"So, we must treat this virus as potentially as severe as previous variants while acknowledging that, as we know, it's even more contagious than previous strains."

Professor Toole said it would also be worthwhile celebrating Christmas outdoors, weather permitting, minimising physical contact with others and avoiding crowded areas.

"Christmas and Omicron, we're living in a perfect storm," he said.

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