"Maintaining a strong border protection, putting the border on high alert - which is what New Zealand has already done - is buying us time," he said.
"If we can buy time we can make better decisions."
First detected in Botswana and reported to the World Health Organisation by South African authorities late last week, the Omicron variant appeared to be more infectious than the widespread Delta variant, though more data was needed before health authorities could be certain how much of a threat Omicron would be, Bunce said.
"We know Delta's a pretty infectious variant of Covid-19, so it's spread, of course, all around the globe.
"The fact that we've actually seen Omicron over the top of that has raised a few flags ... maybe it is slightly more infectious; if it was less infectious we wouldn't have seen it raise above, I guess, the Delta background that we're seeing."
He said the world was in a period of uncertainty regarding Omicron and it would take time to understand more about it and about how vaccinations respond to it.
"The fact that [Omicron] contains about 30 mutations in the spike protein has, I guess, caused concern."
Bunce said immunologists expected it would take one to two weeks to culture a bit of the new variant and to start collecting data on how many breakthrough infections it was causing in vaccinated people.
"It may be more infectious and less pathogenic, but it's an option that maybe it's more pathogenic. We don't know, this is the period of uncertainty.
"Really the acid test comes when we see ... how [Omicron] gets on in a country with high vaccination percentages because we'll see how many breakthrough infections we see."
Bunce said despite the high number of spike protein mutations detected in the new variant, vaccines were "still our best bet".
University of Otago epidemiologist professor Michael Baker agreed with that assessment, telling First Up he thought it was "highly likely" the vaccines would still be effective against Omicron.
While it could turn out the existing vaccines were less effective at producing immunity against the new variant, manufacturers were already thinking about reformulating their vaccines so they were better able to deal with the virus, he said.
While it was "unusual" that Omicron appeared to be outperforming Delta, Baker said it probably wouldn't be more deadly.
But he acknowledged the concerns around the world about the new variant and said any mutations of the Covid-19 virus needed to be taken seriously.
"As we've seen successive new variants become more common, they haven't generally become more dangerous … although maybe in subtle ways.
"Actually, any variant that infects a lot more people, by its very nature becomes more dangerous, because then a whole lot more people get sick, and some will die of course."
Vaccine boosters available from today
Those who had their second shot of the Covid-19 vaccine more than six months ago will be able to get a third booster shot from today.
New Zealand's vaccine rollout began in February this year, so healthcare and border workers, as well as elderly New Zealanders, could now be eligible for a third dose.
The Ministry of Health expects over 455,000 people will be eligible for a booster by the end of the year.
Baker said it was "very important" for people to get a booster as large studies overseas had shown the effectiveness of the vaccines diminished over time.
"As we've observed the effect of the vaccine, which does work extremely well at protecting you from serious illness and death, we do know that its protection against infection does wane over time, and so after six months you really need a booster."
He said it was perfectly fine for those who may have received a different vaccine overseas to receive a Pfizer booster shot in New Zealand.
"There's actually some evidence that you may get an even better immune response if you mix them [the vaccines]. Remember … they're all really targeting the spike protein but they're subtly different in the immunity they generate … there's no problem mixing and mingling them."
