Omicron variant: what do we know about Covid case numbers and combatting it in Australia?

 Melissa Davey Medical editor 1 day agoLike|2Aus officials: Taylor Swift party linked to Covid outbreakHarris says Biden administration ‘didn’t see omicron coming’Photograph: Con Chronis/AAP© Provided by The Guardian Photograph: Con Chronis/AAP

Preliminary modelling showing Covid cases in New South Wales could hit 25,000 a day by the end of January made headlines on Tuesday after the health minister, Brad Hazzard, cited the figure on the same day as more restrictions were rolled back.

While the University of NSW modelling did not take into account increasing booster shots or the potential reintroduction of restrictions if cases grow, Omicron has thrown previous predictions about the efficacy of vaccination and predicted case numbers into disarray.One epidemiologist says uncontrolled spread of Omicron in Australia would lead to hospitals being overwhelmed even if the variant caused milder disease.© Photograph: Con Chronis/AAP One epidemiologist says uncontrolled spread of Omicron in Australia would lead to hospitals being overwhelmed even if the variant caused milder disease.

Related: NSW Covid cases predicted to hit 25,000 a day as state eases restrictions

It is becoming clearer that the variant is more infectious and more vaccine-evasive, so how worried should we be?

What impact is Omicron having on previous modelling and advice?

Early data from South Africa and laboratory data from the Kirby Institute in Australia has found being double-dose vaccinated against Covid-19 does not offer as much protection against symptomatic infection from the Omicron strain as it does for Delta.

The South African research analysed 211,000 positive test results from adults aged 18 and up, 41% of whom had received two doses of the Pfizer vaccine, and found protection from Omicron infection was 33%. The Kirby data placed efficacy similarly, at 37%, regardless of whether the vaccine used was AstraZeneca or Pfizer.

Encouragingly, the South African data found those who had received two doses of the Pfizer vaccine had 70% protection against severe disease and hospital admission. While this is lower than the 93% protection offered against Delta, 70% is still regarded as very good protection.

But it means previous predictions for when a third booster dose of the vaccine might be needed will probably no longer hold. While it had seemed hopeful a booster shot might offer protection for at least one year against the Delta strain, Kirby Institute researchers say it is appearing likely that more frequent ongoing boosters will be needed against Omicron.

Related: Omicron variant expected to become dominant strain in Australia as NSW records 1,360 new Covid cases

This is early data and won’t be the final predictions for how Omicron will behave. South Africa also has a unique context, with low vaccination rates but a high number of people who have been previously infected with Covid, leading to higher rates of natural immunity than Australia which may also lead to differences in spread. But the data is an early indicator that will prove useful to groups like the Australian Technical Advisory Group on Immunisation (Atagi), which advises the government.

Guardian Australia contacted the Doherty Institute, which provides modelling to the federal government, to ask whether new modelling for Australia had been completed, but did not receive a response.

If Omicron causes milder disease than Delta, won’t hospital rates fall?

Not if Omicron is highly infectious and spreads to the most vulnerable too quickly, epidemiologist and public health medicine specialist with the University of Melbourne, Prof Tony Blakely said.

“The best-case scenario is that Omicron comes through in a controlled manner, and infects mostly the people who are unvaccinated, but they get a mild illness,” Blakely said.

“Some of them will die, though not as many as from Delta, and that will mean our immunity is boosted so that in Australia we’ve all either been vaccinated and boosted, or infected with Covid-19, or both.

Related: ‘A shambles’: fears rural and disadvantaged areas will lag behind in Australia’s Covid booster rollout

“Those things together will hopefully get us to a position where we’re very resilient and it’s much easier to live with whatever coronavirus throws at us next. But how to do this in a controlled manner is the big question mark.”

A fast peak in cases would lead to hospitals being overwhelmed, he said, because there will always be those who become severely ill or die. It also appears that some treatment options now being heavily relied upon to reduce deaths in vulnerable patients, such as antibody therapies, might not be as effective at disarming the Omicron variant.

Should other measures be taken?

It would be important to roll out booster shots quickly, Blakely said, and implement measures such as mask-wearing in the meantime to slow and stop the spread among those most susceptible to severe disease such as elderly people, the immunocompromised and the unvaccinated.

“We don’t need to wait on more data and modelling to know this is what we need to do,” he said.

Director-general of the World Health Organization Tedros Adhanom Ghebreyesus said the world could not rely on vaccines alone, and that other public health measures such as mask-wearing, proper ventilation, hand hygiene and social distancing should not be dismissed yet as countries like Australia reopen.

He said he was concerned people might dismiss the risk posed by Omicron because it seemed to cause milder disease in most people.

“Omicron is spreading at a rate we have not seen with any previous variant,” he said. “Surely we have learned by now that we underestimate this virus at our peril.”

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