Director general of heath Ashley Bloomfield appears to be at odds with his own ministry over when the clock starts ticking for the 28-day Covid-free period.

The period is part of the Health Ministry's elimination strategy, which will form a key part of Cabinet's decision on Monday about whether to move New Zealand to alert level 1.

This morning Bloomfield told the Herald that the 28 days was a "moot point" and there was no set criterion, but the ministry said in a statement that the period began on May 18 - meaning it will finish on June 15.

May 18 was when the last community transmission case - where the source of infection is not known - had come out of isolation.

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"As per the definition of elimination, the 28 day period would be counted from that person's exit from isolation," a ministry spokesperson told the Herald.

That case was a Ministry for Primary Industries worker who was asymptomatic, but tested positive on April 29 as part of surveillance testing at Auckland Airport.

There have been more recent cases of Covid-19, but the sources of infection for those cases have been successfully traced.

Health Minister David Clark wouldn't say when he believed the clock started ticking on the 28-day period.

Meanwhile Bloomfield conceded that the country's contact-tracing system - critical for handling a second wave of Covid-19 - remains untested as Cabinet's D-Day for alert level 1 looms.

But that didn't mean the country will not be ready to move to level 1 next week, and Bloomfield says the system will be stress-tested in the coming weeks to ensure it is ready.

He said a move to alert level 1 was likely if there were no new cases between now and Monday, which will be a week shy of June 15.

"We're moving quickly but still thoughtfully. The signs are all good and if we maintain the zeros over these next few days, that will be incredibly encouraging for a possible early move to alert level 1."

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If Cabinet decides on Monday that New Zealand is ready to move to level 1, it could start as early as Wednesday next week.

34 days since the last community transmission case reported

A Cabinet paper, leaked to the National Party, said that moving to level 1 would require 28 days of "no new cases of Covid-19 caused by community transmission".

National Party leader Todd Muller and Deputy Prime Minister Winston Peters have both used the last case of community transmission at the end of April - 34 days ago - as the date to start the clock.

They have called for alert level 1 to have been put in place already, as has Act leader David Seymour.

Public health experts have asked whether the criterion is about the most recent domestic transmission - meaning any infection that is not an imported case - or when the most recent infectious case went into or came out of isolation.

Prime Minister Jacinda Ardern said yesterday community transmission - where the source of infection is unknown - is only one factor for Cabinet to consider.

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Prime Minister Jacinda Ardern and National Party leader Todd Muller verbally sparred yesterday over whether New Zealand should already be in alert level 1. Photo / Getty
Prime Minister Jacinda Ardern and National Party leader Todd Muller verbally sparred yesterday over whether New Zealand should already be in alert level 1. Photo / Getty

Despite the Health Ministry's statement about May 18, Bloomfield said there was no set criterion and it was a matter of looking at all the recent cases and testing data.

"What we're really wanting to assess is our level of assurance and certainty that we haven't got community transmission.

"Our most recent case was 13 days ago, so that's within that two two-week [incubation] period. Our most recent case where we're not certain about the source of infection was the end of April - that person didn't finish their isolation until the 18th of May.

"There's no script for this and there's no bright line."

Another factor to consider, he said, was whether any new infections may have sprung up after the limit on gatherings was increased to 100 people.

That has only been allowed since Friday, but it usually takes 10 to 14 days for any new branches of transmission to show up in testing data.

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Bloomfield said another issue is that transmission can come from surfaces, not just from Covid-carrying people.

"We've seen transmission, particularly in healthcare settings, on fomites and inanimate objects through the environment. We don't want to be too careful but we don't want to be overcautious."

He said he was confident in the key pillars that would need to work well - contact-tracing, border control and testing - before the country could move to level 1.

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Contact-tracing capacity untested

The Health Ministry has gone backwards in terms of the time taken for the end-to-end contact-tracing system.

It is now taking nine days to isolate 80 per cent of close contacts from the first symptoms of the source of a chain of transmission (the index case).

In the first week of May it was taking only five days and the benchmark, as outlined in infectious diseases specialist Dr Ayesha Verrall's audit in April, is four days.

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Bloomfield said part of that process was outside the ministry's hands, in particular people deciding to get tested as soon as they have any symptoms.

The ministry was hitting its key target of isolating 80 per cent of close contacts within 48 hours of a positive lab result.

But the latest data covers alert levels 4 and 3, meaning most cases only had between two or three close contacts, and they were likely all in the same household bubble.

Epidemiologist Sir David Skegg said the system was untested and will be challenged at lower alert levels, and when borders open to Australians and international students.

Bloomfield agreed: "At the moment we are in the position we wanted to be in where we haven't got any cases. But we won't know if our contact-tracing system is going to work when it needs to if we haven't actually tested it.

"We'll be working up stress-testing over the next few weeks."

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Another challenge has been the different IT systems across the 12 Public Health Units (PHUs).

Nine of the 12 will be using the national system by the end of the week, but PHUs in Auckland, Wellington and Christchurch have their own systems, raising questions about whether that could impede containing a new Covid-19 outbreak.

One of the key findings of Verrall's audit was that a compatible system enabled efficient sharing of the workload across PHUs in different regions and the national contact-tracing centre.

Bloomfield said he wasn't concerned because the systems in Auckland, Wellington and Christchurch can "interface seamlessly with our national system".

It would be good in principle to have all PHUs using the same system, he said.

"But it's a question of timing, because it would be a lot of effort and could be disruptive. If we've got the functionality we need by linking their existing systems, that's the most important thing."

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He said the ministry was on track to be able to contact-trace up to 500 cases a day by the end of June.

That was only half what Verrall's report had recommended, but Bloomfield said the 500 was not the end point.

"Our peak daily infections were about 90 - 500 is a lot more than that. If we're able to do 500, we'll have in place an infrastructure onto which we could add more capacity as and when needed.

"That will be the next phase we will do."

He added that a situation where tracing for 500 cases a day would trigger other control measures.

"We wouldn't be in level 1 type arrangements. We want capacity in the system to avoid going back to level 3 and 4 - that's where I think 500 is a good starting point."

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Border controls working well

Bloomfield said with no community transmission, the borders were the most vulnerable area and control measures would be further strengthened.

Everyone arriving from overseas has to be quarantined or put in managed isolation, but the ministry was now looking to test them when they land and again before they finished the 14-day isolation period.

Director general of health Ashley Bloomfield said the marches on Monday, seen here in Auckland, broke the alert level 2 rules. Photo / Dean Purcell
Director general of health Ashley Bloomfield said the marches on Monday, seen here in Auckland, broke the alert level 2 rules. Photo / Dean Purcell

Bloomfield said work was also being done for air crew arriving from Los Angeles, who didn't have to follow the same strict measures as crew arriving from parts of Asia, where they "don't even go into the airports".

He said details were being finalised, but the proposal was for staff flying in from LA to be tested and have a short period of isolation.

That was not part of the proposal for transtasman travel, however.

That travel bubble would not open up until New Zealand could be "supremely confident" about minimising the risk of importing Covid-19 across the Tasman, he said.

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Travellers would not face quarantine on arrival, but would have to fill out a health screening questionnaire and have their temperature checked.

Bloomfield said there had been no positive tests for any hotel, security or health staff involved in managing the quarantine of overseas arrivals.

"That speaks volume to the work that's gone in to keep staff safe around the border."

A Ministry for Primary Industries staffer working at the border had tested positive on April 30 as part of surveillance testing - which Bloomfield said would continue through level 1.

Ongoing testing in areas where it's needed

He said there was no magic number for the right level of testing at level 1.

"The testing will remain very focused on a low bar for testing anyone with symptoms - even if you've got a bit of a sniffle."

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Surveillance testing would concentrate on the border, but it could also be deployed in any area where the ministry felt it was needed, he said.

Previously surveillance testing has targeted supermarket workers, for example.

Bloomfield said he expected testing numbers to climb again as winter gripped the country, as that would lead to people having more symptoms.

"The main thing is people know they should be tested, and they know its free and readily available to them."

Public health experts have been calling for masks to be worn in indoor settings, including on public transport, where the risk of infection is higher.

Bloomfield said the ministry was constantly looking at the issue, including the advice from the World Health Organisation.

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"We'll keep it under constant review. Widespread mask use - we don't think it's required, but that could change in the future."

Outdoor gatherings are considered less risky, but Bloomfield said there was still a danger and people should keep to the 100-person limit during level 2.

He said the public marches on Monday in solidarity with the Black Lives Matter movement broke the level 2 rules, but people who attended didn't need to self-isolate because there was no evidence of community transmission.

"It doesn't mean that we shouldn't still not have those gatherings. That advice stands.

"There was a risk, and that's why we have the limit of 100. The risk is always relative.

"We didn't think there was high risk, and I would expect many people were doing their best, even in that context, to physically distance."

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