28 days Covid-free for

Twenty-eight days case-free. That could be how long New Zealand needs to spend in alert level 2 before we have successfully eliminated Covid-19 and can move down to alert level 1.

Public health expert Professor Michael Baker thinks that, from an epidemiological point of view, two 14-day incubation periods with no evidence of new cases would provide health experts with a ‘‘high level of certainty’’ the virus had been stamped out.

It could be earlier, going by onset dates of recent cases, which were almost always earlier than the reported date. Once elimination was confirmed, the alert levels could relax, the University of Otago professor explained.

Director-general of health Dr Ashley Bloomfield hasn’t put a timeframe on our stay in level 2.

‘‘[Elimination is] not a point in time, it’s a sustained effort, and we know we are going to have to sustain that effort,’’ he said yesterday.

He defined elimination as a sustained ‘‘keep it out, stamp it out’’ phase. This would be done through our ‘‘tight’’ border measures, wide testing, good contact tracing and rapid isolation of contacts.

However, Bloomfield did say that Kiwis shouldn’t expect to be in this stage for months.

‘‘What people should anticipate is we will be continuing to ask them to do the basics, which means that then we’re more likely to be able to keep our cases low, or zero, which means we are much better placed then to consider a move to alert level 1.’’

Prime Minister Jacinda Ardern will set out further ‘‘decision-making milestones’’ for level 2 and level 1 today. Cabinet will review attendance limita

tions for gatherings in level 2 on Monday.

Pinpointing when exactly we could move down was difficult for both Baker and Dr Arindam Basu, an associate professor from the University of Canterbury, to answer. But from a health scientists’ perspective, Basu suggested we could be in level 2 for a while.

‘‘All things considered, in order to avoid a return to stricter conditions, we expect to be in level 2 for a while unless the modellers and epidemiologists with the Government, with more knowledge, can advise an ‘all clear’ and we go down one notch.’’

Thanks to the Government’s ‘‘three-pronged policy’’ of testing cases, contact tracing, and isolating cases and clusters, the likelihood of cases remaining low was very high, Basu said. ‘‘Now, unless the borders are opened again with influx of new cases, the case count will likely remain low.’’

But Basu warned even if we did move down to level 1, it wouldn’t be a return to normal.

‘‘Remember this viral infection takes one person to seed and infect about two to three people and then it spreads fast.’’

Physical distancing and hand hygiene would simply become part of our daily habits.

‘‘The hand-wash, respiratory hygiene awareness that germs can spread by hand-shaking might as well be ingrained as new normal in our society and create a ‘comfortable safety zone’,’’ Basu said.

Baker understood the alert level system was derived from a similar strategy in Singapore. He said it was designed to suppress transmission, but if New Zealand succeeded in stamping it out, they became void.

‘‘Obviously, if you’re convinced you’ve got no transmission in the country any more, well, you don’t really need to be suppressing it actively.’’