It is inevitable new Covid-19 variants such as the newly discovered XE strain will arrive in the country, Director-General of Health Ashley Bloomfield says.

Early studies of the new variant, which has spread in the UK, shows it to be more transmissible than Omicron but its severity is still to be determined.

"It's actually sort of a combination of the BA.1 and BA.2 Omicron subvariants, and there is a sense that it might be around 10 percent more infectious," Dr Bloomfield told Morning Report.

He says wider genomic sequencing will be introduced as the country moves down its security settings.

"Yes, we've got plans for wider surveillance ... the idea here is we pick up a new variant of concern either at the border or very early on in the community."

Wider surveillance testing of other illnesses will also play a role heading into winter, as the borders open up, he says.

"We know they'll be coming back across the border so we will be sort of ramping up that surveillance testing as we head into winter ... it would be mostly through people who are going to get healthcare - so people visiting their GP or visiting another clinic, or arriving in hospital.

"You don't need to do everybody, but you need to do a proportion of people and get a good spread right across the community by age group and geographical region."

'A large and very active Omicron outbreak'

Prime Minister Jacinda Ardern yesterday announced all of New Zealand would remain in the red traffic light setting.

Dr Bloomfield this morning repeated the decision is based on officials' health advice.

"It was on the basis of our advice and our team, which does a review every two weeks, did what they usually do - went through a whole range of data, looked at the various criteria. They did that early last week.

"We've still got a large and very active Omicron outbreak in New Zealand - 13,000 to 14,000 cases a day - yes the numbers are coming down, but also nearly 700 people in hospital around the country and nearly half of those are in Auckland, that's a lot of pressure on our health system.

"Everyone is as keen as anything to get back to normal as soon as we can and that's certainly top of mind for us but it's by no means normal in our healthcare system and that's really where we need to focus our efforts still.

"We want to keep that downward trajectory going."

He says there is no single number that will lead officials to advise a move to orange.

"Not a specific number, there are a few things we're looking at and one of course is not just the number of people in hospital but the number of new admissions each day ... there's still over 350 people in hospital across the Auckland region.

"Only around one per cent of our cases end up in hospital so there's quite a significant number of people who are also being looked after in the community - by general practice, by Māori and Pacific providers."

With indoor gathering limits increased to 200 but hospitality still operating on a seated and separated basis, it may seem perverse that house parties can have up to that number but bars are much more restricted. Bloomfield suggests bars would be harder to contact trace.

"One of the things about a private gathering is there's more control over who comes and so you tend to know who the people are ... it's much easier to let people know if someone turns up a positive test.

"Certainly we've known right from early on in the pandemic that those sort of indoor settings with close contact, a lot of people moving around, those are the places where we do see transmission happening, especially in that age group. We've still got high rates of infection in that younger age group."

-RNZ.