Tuesday 25 January 2022

I hate to say I told you so, but well

This week's column in the Stuff newspapers went through a few things that should have been obvious but only seemed to be recognised the next day.

I wrote:

The country’s Covid testing system is likely to fall apart, quickly, when case numbers rise.

Testing labs can bundle five to ten samples together for testing. If none are positive, all is fine.

If the pooled sample is positive, individual samples need separate re-testing. When positivity rates are low, the system works well. But when positivity rates are high, pooled sampling stops working. Testing capacity drops to a small fraction of what it had been, just when it is most needed.

Headline figures on testing capacity may be more than a little optimistic. Contracting now for greater capacity, focusing on the saliva-based PCR testing (which identifies genetic material from the virus) that catches Omicron cases earlier, matters.

Hopefully it is not too late.


If the PCR testing system fails under the load, a positive RAT result could confirm whether therapeutics are needed. But making sick and infectious people go to a pharmacy for testing while sick and infectious would be a terrible mistake. Policy will need to change.


Omicron has been ripping through schools abroad. Kiwi kids are at greater risk than children abroad because New Zealand was slow to start vaccinating under-12s.

Parents staying home to care for sick kids will likely also catch it. Sick leave entitlements will be burned through.

Making schools safer means hastening vaccination of children and allowing under-18s to receive vaccine boosters.

Better ventilation in schools, and air filtration in harder-to-ventilate places, also matter.

Late last year, the government announced air filtration units were being ordered, along with carbon dioxide monitors that help track whether a room has sufficient ventilation.

No progress has been reported.

Preparation at schools is bad enough that epidemiologist Amanda Kvalsvig recommended that the start of school be delayed.

Waiting for the government to get its act together may lead to disappointment. Parents could move faster in schools that are less well-prepared.

Carbon dioxide monitors are not hard to find online.

Buy one for some in-class experiments, after talking with your child’s teacher.

What is the carbon dioxide level at the start of the day, as children start filing in? By how much does it increase when the students have been in the room together for a while? Does opening windows help much?

A simple student experiment could help the school identify problem areas with poor air circulation.

If there are ventilation problems in your child’s classroom, a second classroom project might help.

Homemade air filtration units, called Corsi-Rosenthal boxes, are easy for older students to build and can help clear the air. Plans are easily found online, though parts can be harder to source.

The blizzard is coming. We had best prepare ourselves.

After I'd submitted the piece on Sunday morning, I saw that Omicron was properly upon us. And, thankfully, that the government was extending covid leave support. 

The Monday column attracted the usual amount of Twitter hate. 

I normally don't point to this stuff. Just par for the course in columning. Every columnist gets it. If you don't like it, don't write columns. 

But it was pretty funny given what happened in the very next day's news.

Let's have a fact check on whether I was right about air filtration in schools not being ready.

Here's The Spinoff, on Tuesday:

The government’s ordered 5,000 portable air cleaners for schools as children prepare to head back to the classroom. But, just 500 will be available in March with the remaining 4,500 due to be delivered by June.

How about that testing system and the problem of pooled samples. That that whole thing will fall apart when positivity rates go up: some right-wing misinformation campaign?

Dileepa Fonseca, on Tuesday:

However, even the 40,000 tests a day figure is likely to be a vast overestimate, because it is based on pooled testing.

Last year in an interview with Stuff, Asia Pacific Healthcare Group chief executive Anoop Singh (whose company is the largest single processor of Covid-19 tests), said “capacity for a large network like us is really not an issue” because tests could always be pooled.

“The pooling ratios will dictate your capacity.”

However, the situation in Australia shows how pooling ratios can drop away very quickly.

During a press conference on December 29, NSW Health Pathology director Dominic Dwyer admitted his state had lost the lab capacity it once had, because it could no longer pool samples.

“Now that the number of positive cases in the community is so high, the ability to do that pooling is limited because you have to go back and re-test them if they are positive,

“So we’ve lost that advantage to maximise our capacity through pooling.”

Igenz laboratory director Amanda Dixon-McIver, whose lab is contracted to process saliva tests for Rako Science, says pooling ratios in New Zealand can run from 1:2 to 1:8.

“In a scenario where you don’t have widespread community transmission then the use of pooling is perfectly OK because it does conserve your reagents.”

To get an idea of how the country’s testing capacity might be affected when pooling falls away, imagine a scenario where those 40,000 tests had been pooled at a ratio of 1:4.

If you were not able to pool it would mean you were suddenly only able to run 10,000 tests.

I've seen the occasional twitter conspiracy theories about Dileepa's reporting on this stuff, so here's another piece making the same point, also on Tuesday.  

The Ministry said labs were able to process 42,000 tests on a daily basis, with a surge capacity of 62,000, and plans were in place to ensure they continued to operate during community spread, but it declined to elaborate on what those plans involved.

Taylor said that processing even 40,000 tests a day was a stretch because a rise in positive cases prevented labs from “pooling”, the practice of processing batches of five to eight samples at once, and only doing individual tests if a batch returned a positive result.

“If you get a 30 per cent positivity rate, you can’t do that, so that instantly drops your ability to test really quickly.”

Funny that an obvious point made in an oped column attracts the hate, then reporters go and check on things, and find that we will indeed fall over in the same way that Australia fell over - which should have been really obvious to everybody much earlier. 

Wish I had been wrong. 

Meanwhile, bless poor Doug Hitchon from Mahana. 

He doesn't know that the government banned importing RATs until real recently, and now heavily restricts how they can be imported. So he blames private enterprise for failing to get them in. 

And he also doesn't know that the government, back in October, set legislation giving itself the power to requisition any equipment that testing labs might import - so it would be an awfully charitable company who would spend a lot of money expanding their lab capacity. 

Democracy's the theory that the common person knows what he wants, and deserves to get it good and hard. We're going to be getting it good and hard for pretending for far too long that the border system could never fail and so there was no urgency in getting anything else ready.

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