A review of the February Covid outbreak found a lack of coherency among central agencies, conflicting messaging that could undermine public confidence, and a Government that had failed to learn the lessons of past reviews.

The February review - by the independent advisory group chaired by Sir Brian Roche - also found a lack of stress-testing the system, and ongoing uncertainty about the system's ability to handle a large outbreak.

The February outbreak had 15 cases, was centred around Papatoetoe High School, and saw Auckland put into level 3 lockdown twice in two weeks.

It also saw conflicting comments when Prime Minister Jacinda Ardern accused a KFC worker of being irresponsible by going to work, while the worker said she had not been told to stay at home.

In a May letter to Covid-19 Response Minister Chris Hipkins, Roche said his group's review found a number of areas that needed improvement.

And some of them had been issues for some time.

"While recommendations have been made multiple times from earlier reviews, scenario planning has not been carried out," Roche said in his letter.

"The lack of clarity about the system's capacity to handle a large outbreak was identified in previous reviews and remains a high priority to be resolved and acted upon.

"We consider as a matter of priority that a full stocktake be undertaken of what has been actioned, what hasn't and why, and what the timeline for addressing them will be."

In particular the system needed to be stress-tested, the review said.

"To solely rely on lessons from actual outbreaks is unnecessarily risky."

It said the ministry wanted to view system capacity in terms of contacts that van be traced, but "the present capacity has not been clarified".

"We do not accept that it is reasonable to not have clarity on the capacity of the Covid-19 Response System on the basis that it is complicated," the review said.

The system would struggle to stay ahead of a large outbreak of 100 to 200 cases a day while the population was mostly unvaccinated, it said.

"We do not agree with the Ministry's assertion stated to us that it is not necessary to increase the standing or surge capacity in New Zealand, or the assertion that this is not possible because there is a lack of an available workforce."

Roche noted a lack of clear messaging in February as another key issue that needed attention, including how the terms "casual-plus" and "close-plus" had muddied the waters.

He said the Ministry of Health should only use "close" and "casual" contacts, but for the recent Wellington scare the ministry used the new terms again - before eventually removing them from its website.

"It is important to get the timing and content of messaging as clear and simple as possible," Roche said in his letter.

"We cannot afford to lose the confidence and trust of the public by creating unnecessary complexity or airing conflicting messages."

The review said there was no evidence in favour of the new definitions, nor any external review or advice.

"More than 1600 casual contacts were relabelled as close contacts, with no mechanism for determining the actual denominator. Given the requirements for close contacts, this is suboptimal," the review said.

"GPs found the new definitions unworkable in practice, abandoning them when deciding who they should test as they found them too restrictive. Members of the community also found the definitions confusing, which contributed to 'non-compliance'. This was a particular problem when members of the same household were placed in different categories."

Roche also recommended a stronger role for public health units in leading the response to an outbreak, which at the time was a complex web of central government agencies, operational agencies and ministers.

"This can lead to a lack of clarity where it comes to accountability and decision-making responsibilities," Roche said in his letter.

"The lack of coherency between central agencies in terms of messaging, instructions and leadership has caused uncertainty and confusion for broader stakeholders such as businesses."

He also wanted a stronger role for independent science advice - which Professor Michael Baker, a member of the ministry's technical advisory group, has been calling for for months.

"We strongly recommend that there is formal input of external scientific expertise through established processes to incorporate external expert peer review and advice," Roche said.

And care also needed to be taken so the workforce didn't burn out, he said.

"The stretched workforce and general signs of weariness and fatigue together with system capacity issues are of particular concern.

"Experience suggests that when such behavioural conditions prevail, the ability of the system and those involved to innovate and adapt is compromised. This puts the operating model at significant risk."

The group also recommended interventions to ensure equitable access to services from Maori, Pasifika, and those in south Auckland.

Other members of the group include businessman Rob Fyfe, Chief Advisor Pacific for the Ministry of Health Dr Debbie Ryan, epidemiologist Professor Philip Hill, and public health expert Dr Dale Bramley.

Hipkins said many of the recommendations have already been actioned.

"Some of the key insights in this report are being taken on board or have been superseded and others are being worked through.

"As the group acknowledges, relationships and coordination across the health system and into the community has improved from earlier outbreaks."