Dr O'Neale said looking to Australia was useful in trying to determine what would happen if Omicron got into the community in New Zealand.
"They're very similar to us in that they're in the same season and they've got similar levels of vaccination to us at the moment, and depending on which state in Australia you look at, we've seen these really rapid growth rates with really short doubling times, in the order of two to three days before case numbers are doubling and going from hundreds to thousands to tens of thousands of cases every day very quickly."
Dr O'Neale said New Zealand should try to delay Omicron from getting into the community for as long as possible and use that time to prepare for it.
He said that would involve eligible adults to take their booster and getting children vaccinated.
"But also things like sorting out our supply chain for things like good quality P2 or N95 masks, so making sure people have access to those, making sure there are rapid antigen tests lined up."
The Ministry of Health briefing yesterday said that 36 per cent of those who were eligible for the booster dose have now had it.
Workplaces should also ensure they have contingency plans for the potential to have large numbers of staff not able to come into work because they are isolating, Dr O'Neale said.
This had been a significant issue in other countries with industries being forced to close because they had so many staff isolating, he said.
Yesterday's low number of cases was likely to be due to a number of factors, he said.
"Over the summer period people have really changed their interaction patterns, [we've got] schools are closed, most people haven't been at work for a couple of weeks and this coincided with a time when we had low numbers going into this.
"We also had a large fraction of the population very recently vaccinated - so this is when people are at their peak immunity, the vaccine's most effective."
But he said the number of cases were likely to creep up once the immunity provided by the vaccine started to wane a little and people returned to work and schools.
Dr O'Neale said being outside, as people were during the summer break, was a great way to prevent transmission of the virus, whereas being inside in an air-conditioned environment was a good way to increase its transmission.
He said it was unlikely that Delta could now be eliminated from the community.