New Zealand could create cordoned-off "safe havens" to protect our elderly and vulnerable if the country fails to stamp out Covid-19, experts say.

It's hoped New Zealand will become one of few nations in the world to head off the virus through a hardline approach of elimination that has started with a four-week lockdown.

But if the effort flops, the country would be forced to fall back either to "mitigation" – where it could try to build herd immunity while trying to protect its vulnerable – or "suppression", where tougher measures like prolonged lockdowns would be needed to squash down spread.

In an editorial in today's New Zealand Medical Journal, a group of University of Otago researchers suggest that failing to contain the pandemic could involve having to roll out a "safe haven" programme from region to region.

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Public health professor Nick Wilson told the Herald the country could even look at creating sectioned-off "islands" within communities where vulnerable people could be relocated until a vaccine arrived.

"You are talking about an area that is excessively protected. You'd want to have a minimal level of disruption, so there would be an emphasis on supporting people to stay in their own homes and making those micro-safe havens," he said.

There are 71 new cases of Covid-19 in New Zealand. The 71 cases are made up of 49 new confirmed cases and 22 new probable cases. It brings the total to 868 cases in New Zealand since the pandemic began.

"Or you could build up aged-care facilities, or have areas within whole communities."

Wilson said the strategy - called protective sequestration in public health - could involve a cordon, relatives being able to enter to drop off food, and carers living on site.

"During the Sars pandemic in Canada, for instance, there were havens where hospital staff were living on-site with vulnerable people so they weren't spreading infection back to their families.

"This approach would also have to be entirely voluntary, because people would have to stay on these islands for some weeks or months until elimination was achieved, or the pandemic was over.

"These are ideas that are worth exploring, because this is a disease that is so different for different age groups."

Figures calculated by Wilson and his colleagues showed the risk of death for infected people older than 80 was about 250 times higher than for people in their 20s – and 23 times higher among people aged over 60.

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One modelling study suggested 89 per cent of deaths from a pandemic spread in New Zealand would be in the 60-plus group.

They also pointed out the impact of continued lockdowns on younger workers and the economy in general, noting how unemployment rates in the US could jump from 3.5 per cent to between 10.5 and 40 per cent as a result of the shock.

"Other work we've done has shown you could save about half the number of Covid-19 deaths if you focused on protecting the elderly, along with people who have chronic conditions."

Fellow University of Otago epidemiologist Professor Michael Baker said experts pitched the strategy in February, when they feared it would prove impossible for New Zealand to eliminate Covid-19.

"We really wanted to promote as we thought this was going to be an unstoppable pandemic wave, and we also knew the risk was intensely focused on older people," Baker said.

"But we were kind of shot down at the time. Someone remarked that 'this isn't 1918'. But actually, now, we are more like 1918 than we'd hoped."

Baker saw two clear benefits from the strategy: improving people's chances of survival, and easing pressure on the health system.

"All groups can benefit from this – it just requires a lot of forward planning."

How NZ can stamp out Covid-19

In the editorial, Baker, Wilson and colleagues Dr Amanda Kvalsvig, Dr Ayesha Verrall and Dr Lucy Telfar-Barnard, set out just what would be needed to make elimination successful.

New Zealand had made a "large, upfront sacrifice" in pursuing the strategy, they said, and what happened over the next few weeks would prove whether it came off.

"To justify this sacrifice, we need to put maximum effort into giving this intervention the best possible chance of success."

They singled out key measures as border controls and quarantine for incoming travellers; fast case detection, widespread testing and swift contact tracing; strong promotion of hygiene, such as hand-washing; and "intensive" physical distancing, such as the current lockdown, which could be relaxed if elimination was working.

Focus: How to stop the spread of coronavirus. Video / AP / Mark Mitchell

They also suggested smartphone technology to speed up contact tracing, along with greater use of face masks so infected people who were pre-symptomatic had less chance of spreading the virus.

"At the same time… steps need to be taken to reduce impacts of the pandemic on the health system and healthcare workers if achieving success with elimination is prolonged," they said.

They included expanding intensive care unit and ventilator spaces, along with the public health workforce in general.

"The exit path will need to be based on demonstrable high-performing border controls and case and contact follow-up, along with sufficient testing and surveillance to detect a low risk of Covid-19 circulation in the population," they said.

"Under these circumstances, the 'lockdown' can be gradually relaxed, potentially on a regional basis."

Covid19.govt.nz: The Government's official Covid-19 advisory website