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A researcher behind some of the modelling helping the Government fight Covid-19 thinks the rate of new cases needs to drop to almost zero before it is safe to ease restrictions.

Canterbury University Professor Michael Plank, along with other researchers,  has been working long hours helping model how Covid-19 might spread in New Zealand.

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After working on new modelling which helped inform the Government's decision to go to alert level four, Prof Plank told the Otago Daily Times it was "quite possible" New Zealand would be under alert levels three and four for "for some time until a vaccine is available".

Even if New Zealand was in a position to drop alert levels at the end of the four weeks, New Zealanders should be prepared for a "new kind of normal" as the world continues to face the Covid-19 pandemic.

Prof Plank answered the following questions from online editor Vaughan Elder.

1. Can New Zealanders expect life to go back to normal after the four weeks of alert level four and if not then when?

We need to prepare for the possibility that life may not go back to normal after four weeks. Regardless of what happens in New Zealand, the whole world is in the midst of a pandemic that is going to take a lot longer than four weeks to get through, and that will have an impact on what happens here.

Even if we can go down to alert level three in a few weeks time, we are all going to have to get used to a new kind of normal.

2.According to your modelling how far will case numbers likely need to drop before it is safe to drop the alert level?

Ideally we would need to be confident there are no cases left out there in the community, which will require a big testing effort and a drop in new case numbers to no more than a handful. We won’t know whether that’s realistically achievable for the next couple of weeks.

3.And how much would case numbers need to rise before it is a good idea to raise alert levels again?

Again it’s too soon to say. When the Prime Minister announced we were moving to level four on March 23, we had less than 100 cases. Now just seven days later we have 514, and it will be a lot more than that by the time the effects of level four kick in. That gives you an idea how quickly the numbers can go up if left unchecked, so we need to act early to stay ahead of the curve.

4. Can you briefly explain your paper, what is new about it and the different scenarios it plotted?

We looked at two different ways of tackling the spread of Covid-19. The first is to let the disease to spread, but try to slow it down so it doesn’t overwhelm our hospitals. This is the so-called herd immunity that the UK government briefly adopted, but has since moved away from. The second approach is to try to eliminate the virus or at least suppress it until a vaccine comes along.

5. What is the difference in the number of cases and deaths between the different scenarios?

The herd immunity approach, even under a best-case scenario, is likely to cause a 60% infection rate and tens of thousands of deaths.

The suppression approach, if it works, could reduce this to a small fraction of what it would otherwise be. But it means tough level four control measures like we are currently seeing to keep the spread contained.

6. How is the modelling you are working on being used to inform the Government's response to the pandemic and decisions on what alert level NZ should be in?

I think the scenarios we looked at helped convince the Government that tough and rapid action was needed to prevent the worst-case scenario. We are working on more detailed models now to look at questions like when and if can the level four measures be relaxed.

7. What unique attributes about NZ make it easier for us to suppress the epidemic?

Compared to other countries, we still have a relatively small number of cases, which means we can do contact tracing.

This is where health officials interview people who have tested positive about their recent contacts, and then test and isolate those contacts as needed to break the transmission chains.

Also being a small island nation in a large ocean means our border is relatively easy to control, allowing us to stop new cases coming in from overseas.

8. When do you think the number of cases will reach a peak and turn around?

It’s likely to be at least two weeks after we went to level four because there is a lag between people catching the virus and developing symptoms and then getting tested.

The cases being announced today could have caught the virus two weeks ago, before New Zealand introduced any travel restrictions or moved to alert level 2.

9. Based on your modelling are we likely to see things return to normal after four weeks, or will we likely see more periods of alert levels three and four until a vaccine is developed?

A lot depends how our case numbers track over the next four weeks, which will tell us how effective the border controls and level four measures have been. It’s quite possible we will see alerts levels three and four for some time until a vaccine is available.

We are working on models that will help us decide when we could move between alert levels, but we won’t know how long this could take until we see how case numbers trend over the next two to three weeks.

10. Based on what you know now are there things the NZ Government and other governments around he world should have done differently?

With the benefit of hindsight, there are always things that could be done differently. But when events are moving so quickly, doing something good now is often better than doing something perfect a week later. I’m proud of our government’s response so far, it has acted decisively when it needed to.

11.So far only a few cases have required ICU treatment - is this a sign that we are finding a high proportion of cases and that contact tracing is working?

That’s definitely one possible explanation – we’re still in the very early stages of the pandemic where we can do testing and contact tracing for all our suspected cases. But we can’t rule out the possibility that there are still undetected clusters, which is why it’s so important everyone follows the Prime Minister’s advice: behave as if you have Covid-19.