Covid-19: Up to half of NZ population could become infected with Omicron - Modeller

Omicron could infect half of all New Zealanders within a few a months, says a leading data modeller.

The highly-infectious Covid-19 variant is circulating in Auckland, and possibly in the Nelson-Marlborough region, with experts saying it would likely appear elsewhere in a few days.

Covid-19 data modeller Michael Plank said, once it gathered momentum, it could spread very quickly.

"It's certainly possible that once an Omicron outbreak really gets going that we could see a significant proportion of the New Zealand population get infected - it could be up to half," he said.

That could take about four months from when cases started to rise exponentially, with a potential peak after eight weeks, and more people infected on the way down.

But he stressed the figure of 50 percent was not set in stone.

There was a lot of uncertainly about how the virus behaved because it had only been on the world scene for about eight weeks - and public health measures could have a big impact on the outcome, he said.

"The actions we take now and over the coming weeks could reduce the number of people who get infected and it could be a significantly lower proportion," he said.

"We're looking at many thousands of cases a day," Epidemiologist professor Michael Baker told First Up.

"That number will be pulled down for example if there's widespread use of masks and people avoid being indoors with other people."

Omicron transmits very well indoors between people, he said.

"If you are in a room full of unvaccinated people they have a higher risk of infecting you than otherwise.

"New Zealanders don't have any immunity to this virus at all because we haven't, fortunately, had it circulating widely, so it does mean the only way to get protected is to have a vaccine."

If kids under five were indoors with other children, the virus could transmit very widely, he said.

"That will be an issue for preschool settings and that's probably one of the main areas of transmission that we're going to see because it's a group that won't be vaccinated."

The prime minister said the government was planning for scenarios of up to 50,000 cases a day to make sure it was well prepared, but stressed it was not based on modelling.

Auckland's three district health boards were predicting a 1800 cases a day for the city at the outbreak peak, expecting to see that in March.

Baker said it would be just a few days before Omicron started to surface in other parts of the country, after a family from Nelson-Marlborough and a flight attendant tested positive this weekend.

He very much agreed with microbiologist Siouxsie Wiles who said that the red traffic light setting wasn't enough to deal with Omicron.

"We put the whole country into the red light which is fine at the moment but we don't have anywhere else to go after that if we get very widespread transmission, which we will see."

He wanted the government to consider putting alert level 2-to-3-style lockdowns back on the table if the virus gathered momentum too quickly.

It should also shorten the time people needed to wait for a booster from four months to three months, because that could stop people getting very sick and slow the spread, he said.

Professor Michael Plank told Morning Report the more people who get a booster sooner, the better.

"Of course that has to rely on the health advice and the safety data but from a pure modelling point of view, the sooner the better."

He said the red traffic light setting may not be enough on its own but would slow things down and flatten the curve.

"And all of those things take pressure off the health system. We may need additional measures but following those basic measures that we have in place now will make a difference."

Director-General of Health Ashley Bloomfield said his teams would consider the booster issue next month, as well as whether to shorten the gap between doses for under 12s.

The government has continually ruled out lockdowns now that the traffic light system is in place.

Professor Baker said while Omicron looked to be less harmful than other variants, there would still be people who would get very sick and die.

Even those who got mild symptoms could feel very unwell and should be prepared, he said.

"This infection is extremely unpleasant for many people - it's like the worst head cold you've ever had. So, people need to have stocks of basic medicines like paracetamol and anti-inflammatories," he said.

Anyone due for their booster should get one now because it could be just two weeks before the virus was much more widespread, he said.