A new Covid-19 variant is expected to become the dominant strain in the community within weeks as cases surge and an expert warns we could be "losing the arms race with the virus".

University of Otago epidemiologist Professor Michael Baker has again urged Kiwis brace for the second Omicron wave as the community case average increases by almost 50 per cent in nine days.

Otago University epidemiologist Professor Michael Baker. Photo / Supplied

Baker described the 49 per cent increase of the seven-day rolling average of cases on June 25 (4737) to today (7046 ) as an "abrupt rise" and indicative that New Zealand could be at the beginning of another infection wave.

Earlier today, health officials reported 6498 community cases, a further eight deaths, and 487 hospitalisations. The weekly rolling average of hospitalisations has increased from 335 this time last week to 420 today.

"It's a dynamic, a battle between us and the virus and there are factors mainly favouring the virus at the moment," Baker said.

Meanwhile, health authorities have urged people wanting to visit others in hospital to stay away if they are unwell after evidence showed visitors to Auckland's North Shore Hospital passed Covid-19 on to patients.

"This has created a scenario in which patients have then transmitted the virus on to other patients in their room or ward."

Baker said he believed New Zealand was at the beginning of a second wave and this new variant would probably be playing a big role, however, there were other contributing factors as well.

This included the population's waning immunity, the colder, winter conditions, relaxed public health measures, and the sense of Covid-19 fatigue.

"This virus - particularly Omicron - is showing a great ability to keep producing subvariants that evade prior immunity.

"If we are in an arm's race with the virus, well, we could actually be losing it at the moment because we haven't made our vaccines yet, or even our boosters, to deal with Omicron so we're not really getting ahead of it at the moment."

Baker said vaccine manufacturers had completed successful trials showing reformulated vaccines could provide additional protection against BA4 and BA5.

Vaccine reformulation was a process that happened often with Influenza vaccines to ensure they provide protection against the latest strains, and a similar strategy may be needed to stay ahead of Covid-19, he said.

BA.5 is a sub-variant of Omicron and was first detected in New Zealand along with other sub-variants BA.2.12.1 and BA.4 in April, 2022.

The Ministry of Health said these sub-variants would likely replace the current dominant strain, BA.2. Baker said these BA.2.12.1, BA.4 and BA.5 accounted for around half of the variants at the border and a quarter of the variants found in circulation in New Zealand.

Baker said new sub-variants of Omicron were mutating enough to evade our existing immunity. Prior Covid-19 infection probably would not offer a great deal of protection against the new sub-variant because the infections were probably caused by BA.2, he said.

"Just like BA2 took over from BA1, BA5 is going to do the same."

Of the people whose deaths with Covid-19 were reported today by the health ministry, one was in their 60s, four were in their 80s, and three were aged over 90.

Three people were from Auckland, two were in Waikato, one was from Taranaki, one was from MidCentral and one was from Whanganui.