Saturday, December 4

With blocks decreasing for the rest of New Zealand, Auckland becomes the first elimination line


By Michael Plank and Shaun Hendy de The conversation

The conversation

Analysis – The number of new cases in the New Zealand delta outbreak is now on a downward trend and we have a good chance of eliminating it, even as lockdown restrictions ease for most of the country starting tomorrow.

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After a spike in the number of cases during the weekend of August 28-29, the Ministry of Health reported only 20 new cases for three consecutive days, of which most were already isolated during their infectious period.

This downward trend shows that Alert Level 4 restrictions and contact tracing are working, reducing the effective breeding number of the Delta variant well below 1.

Our latest estimates suggest that the R number is approximately 0.4, very close to the value observed in the Outbreak from March to April 2020, the last time the whole country was under the strictest blockade.

We know that Delta is up to twice as infectious as the original wild-type variant, but level 4 blocking measures are proving as effective so far.

This is perhaps surprising given that two Australian states, New South Wales and Victoria, have failed to control Delta outbreaks. The R number in NSW has been consistently above 1 for over two months, leading to a record number of infections and health system under considerable pressure.

New Zealand can still eliminate the current outbreak, but with the Delta variant, nothing is guaranteed and we cannot be complacent.

Additional safeguards

Starting Wednesday, the restrictions will be eased for New Zealanders living outside of Auckland. The new “Delta Alert Level 2” has some additional safeguards, including mandatory mask use and record keeping, a two meter distance in most public places, and a gathering limit of 50 people indoors and 100 people. outside.

Some will be frustrated by the restrictions in place since there are no current cases in many parts of the country. But it is important to remember that we cannot isolate Auckland from the rest of New Zealand completely.

Essential workers still need to travel and goods must move across the country to keep supermarkets stocked. Regular essential worker testing Who needs to cross the border to reduce risk has been introduced. But no limit is airtight, and the fact that most regions have remained Covid-free so far does not guarantee that a case will not arise.

The additional restrictions will reduce the risk of propagation of events such as the ones that triggered the crash. This is key to avoiding another explosive outbreak in a different part of the country, which could send us all back where we started.

Even with the added restrictions, Alert Level 2 is unlikely to prevent an outbreak from growing, so this is a calculated risk. We need higher community testing rates in all regions. Combined with more extensive sewage testing, this will help us catch any case escaping from Auckland before it has a chance to spread too far.

How much longer does Auckland wait

If the virus were to reach essential workplaces, it could cause a resurgence and significantly prolong the outbreak. Both New South Wales and Victoria appeared to have their outbreaks in the Delta under control, only to see the number of cases rise again as the virus spread among essential workers.

The best way to avoid this is to reduce the case numbers as quickly as possible. That means everyone does their bit to stop the virus from spreading. In other words, Auckland residents will have to stick to their bubbles.

Following the current trend, case numbers could be in the single digits next week. If all the new cases are close contacts who have been isolated during their infectious period, Auckland can safely go to alert level 3 at that time.

However, it is also possible that the shoot has a long tail. Every time Delta finds its way to a new home, it tends to quickly infect everyone in that bubble. This could lead to a significant number of new cases and prolong the outbreak. Again, denying the virus the ability to find new bubbles to infect is the best way to eradicate it quickly.

The transition to lower alert levels is a dangerous time. It only takes one box to slide in and turn on an uncontrolled drive chain. Better to wait a few more days at the highest alert level than risk a resurgence that could delay us for weeks.

If we continue to do what we are doing, we have an excellent chance of eliminating this outbreak. This is our best strategy, as it will minimize health impacts and give us the opportunity to live in relative freedom while we complete the launch of the vaccine.

As experience in Australia shows, we have to get it right the first time. We may not have a second chance with Delta.

* Michael Plank is Professor of Applied Mathematics at the University of Canterbury and Shaun Hendy is Professor of Physics at the University of Auckland.

Disclosure statement

Michael Plank is affiliated with the University of Canterbury and receives funding from the New Zealand Ministry of Business, Innovation and Employment (MBIE) and Te Pūnaha Matatini, New Zealand’s Center of Excellence for Research in Complex Systems.

Shaun Hendy is affiliated with the University of Auckland and has received funding from the Ministry of Business, Innovation and Employment (MBIE) and Te Pūnaha Matatini, the New Zealand Center of Excellence for Research in Complex Systems.




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