Were we right to leave lockdown so early after the Valentine's Day cluster was first discovered? And was our return to lockdown a result of anything more than bad luck? Marc Daalder reports
Ashley Bloomfield and Jacinda Ardern fronted a press conference on February 17, three days after Auckland plunged into Level 3 lockdown upon the discovery of three community cases of Covid-19, with good news.
"I can also say there were over 17,000 swabs taken around the country yesterday, many across Auckland. So this is very helpful in terms of us being able to rule out wider chains of transmission, along with our wastewater testing by ESR in Auckland, which has shown negative results. This is reassuring," Bloomfield said.
Ardern added: "Between midnight Sunday and 10 am this morning, I think it’s a total, now, of over 23,000 tests that have gone through. We’ve also carried out wastewater testing in Auckland, and so far the results we have have been negative."
"Based on our usual criteria, the Director-General of Health has recommended to Cabinet, and Cabinet has agreed, that as of midnight tonight, Auckland will drop down to Alert Level 2."
Then, just 10 days later, Ardern and Bloomfield returned to the Beehive Theatrette with grim faces. A new case had been identified without a clear link to other cases, and they had been in the community while infectious for the better part of a week.
"Based on this, we are in the unfortunate but necessary position of needing to protect Aucklanders once again. That is why Cabinet met this evening and made the decision that Auckland will need to move to Alert Level 3 for seven days."
This was the cardinal sin of the Covid-19 response, the mistake that Ardern always strove to avoid: yo-yoing in and out of lockdown. So, was the Government wrong to leave lockdown so early the first time around? Did wastewater and surveillance testing fail us?
Leaving lockdown risky
On February 17, most health experts were surprised by the Government's decision to move Auckland down alert levels, saying it involved a greater degree of risk-taking than officials had hitherto been comfortable with.
"It’s no secret that I would have preferred for Auckland to stay at Alert Level 3 for a couple more days until all the test results had come back. But, the decision by the Government to move Auckland to Alert Level 2 and the rest of the country back to Alert Level 1 suggests they are confident the outbreak is under control and any further transmission can be limited using the test-trace-isolate strategy," University of Auckland microbiologist Siouxsie Wiles said.
"Despite some reassuring results, stepping down Alert Levels does introduce risk because there’s less protection against unknown transmission from potential earlier missed cases," University of Otago epidemiologist Amanda Kvalsvig added.
Kvalsvig's colleague at Otago University, epidemiologist Nick Wilson, was more critical.
"This shift in Alert Levels is not cautious enough from my public health perspective, and also from an economic perspective given that regaining successful elimination is also best for the economy. We still don’t have any clear idea how the pandemic virus got through the border and many test results are outstanding," he said.
The main concerns of epidemiologists revolved around two issues: Whether the source of the small outbreak had gone on to infect other people, who were now themselves undetected community cases capable of spreading the virus; and whether the cases we had identified had managed to pass it on to other people who had not been identified as close or casual contacts.
The Government, evidently, felt that any significant community transmission had been ruled out. That wastewater testing returned a negative result was reassuring, as was the failure to discover any cases via mass testing of symptomatic people in Auckland. This indicated that we were in a very different position from August, where there were dozens of undetected cases in the community when the first person tested positive.
Is wastewater testing a waste of time?
Wastewater testing, in particular, has come in for criticism after the return to lockdown. Why did it fail to detect that there were still active infections in the community, in two families who were not identified until after Auckland stepped down to Level 1?
Dr. Brent Gilpin, a Christchurch-based expert for the national lab testing agency ESR, told Newsroom wastewater testing is not as sensitive as some people assume.
"Wastewater testing is certainly not guaranteed to only pick up one or two cases," he said.
"It's certainly not a failure, it's really designed to pick up a larger community event and situations where you have people who become symptomatic but haven't actually got tested."
"It doesn't tell you that there aren't any cases in the community, it just tells you there's not lots of cases in the community," - Brent Gilpin
In specific terms, ESR expects to receive positive results once there are 10 cases in a population of about 100,000 people. Tests it runs on wastewater from the Jet Park quarantine facility almost always come back positive. Further down the sewage system, where the Jet Park waste mixes with sewage from 130,000 other Aucklanders at the South Western Interceptor, samples test positive around two-thirds of the time. This often depends on how many people are currently ill with the virus in the Jet Park facility.
Given this, a positive result is indicative of fairly widespread community transmission - at least when compared to our normal, Covid-free situation. A negative result, Gilpin cautions, doesn't mean there aren't cases out there. It just signals that there aren't dozens of undetected cases.
"It doesn't tell you that there aren't any cases in the community, it just tells you there's not lots of cases in the community," he said.
"The value is certainly an added tool. And I think if we had been detecting SARS-CoV-2 in the sewage last week, that may have swayed a different decision. The fact we didn't detect it, I have no idea how much weight the Government gave to it, but I think it just really imports that there's not lots of cases in the community that we didn't know about."
Looking at the record thus far, the wastewater testing was correct. It wasn't a large number of undetected cases that forced Auckland back into lockdown, but rather a single case who visited high-risk locations while symptomatic.
'Bad luck'
Instead of looking to testing, experts suggest, we should look at contact tracing and isolation. There appear to have been several breaches of health guidelines in the latest cluster, with people going to high-risk locations when they were meant to be isolating and one violation of the Level 3 restrictions when people from two different bubbles went on a walk together.
The confusing communications and messaging to some parts of the school community didn't help either. It meant that one of the other factors the Government relied on in stepping down alert levels - that contacts of cases who were likely to test positive were isolated - was not in fact reliable. Plus, as in August, the response was hindered by symptomatic people not getting tested or getting tested later than they should have.
"The outbreak proved harder to control than usual with the contact tracing system because of a number of factors. There was an element of bad luck," Otago University epidemiologist Michael Baker told Newsroom. Although he thought at the time that the decision to step down was risky, he now thinks it was the right move with the data and information available to Cabinet.
"The contact tracing appeared to work reasonably well, it's just that amongst the tiny portion of people who were not tested, unfortunately, included the infected families."
While New Zealand's response has often benefitted from a dose of good luck - many of our community outbreaks have fizzled out without many people getting infected, for example - this may be our first bad luck outbreak, Baker suggested.
"It could have, in most circumstances, been a successful approach. It just proved that the simple outbreaks with a clear source, or appear to have a clear source, in general the contact tracing works well enough to manage them effectively. But then if you throw in some compounding factors and some bad luck, that may not always be enough," he said.
"We are learning from these events. It is important that the public understands that if we're trying to move towards managing the disease in the least disruptive way possible, it does mean taking a degree of risk with these situations.
"And if we collectively get it wrong - and we have to get it wrong sometimes - to say that's partly the nature of learning how to manage this pandemic and to get better at it."
