The XBB.1.5 variant of Covid-19, also known as 'Kraken', has been detected in New Zealand, says the Ministry of Health.

Whole genome sequencing results for two Covid-19 cases with XBB.1.5 were reported by the Institute of Environmental Science and Research late last week.

"The detection of XBB.1.5 is not unexpected, following its recent detection in Australia and globally, and our Covid-19 response accounts for the emergence of new variants," says the ministry.

Kraken was descended from the Omicron XBB subvariant, itself a cross between two earlier strains: BA.2.75 and BA.2.10.1.

The World Health Organisation says it has been detected in at least 31 other countries.

While it was difficult to establish whether this variant would become the predominant one in the community, the ministry noted the proportion of cases in the USA with this variant had been "rapidly increasing" since its detection there in October last year.

"XBB.1.5 appears to be outcompeting other XBB sub-lineages and BQ.1.1 in the USA," says the ministry.

"It remains unknown how XBB.1.5 will compete against other variants in a New Zealand context, and whether this could affect the level of Covid-19 circulating in the community in the coming months.

There's no evidence at this stage to indicate XBB.1.5 causes more severe disease compared to other variants, says the ministry.

But New Zealand had a high level of immunity due to high vaccine uptake and the recent wave of infections, says the ministry.

"Vaccines are still expected to provide protection against severe disease from XBB.1.5, particularly in those who have received boosters.

"We encourage people to get their vaccine and booster doses when they fall due."

University of Auckland associate professor Dr Siouxsie Wiles says there's concern over XBB.1.5's mutations which are "better able to infect and evade immunity from vaccines".

"Often by the time it is identified in a country, it moves."

But New Zealand has tools to reduce the impact of the new strain, says Wiles. Her advice is simple.

"I would be advising people to wear masks on public transport and planes, malls, supermarkets, wherever you are around people."

As with previous strains, Wiles says people's experiences are very different with some getting very ill and others largely unaffected.

The Ministry of Health on Monday reported 2424 new cases of Covid-19 in the community - down about 100 from Sunday and just over half the 4000 cases reported on January 4.

-RNZ.