Plagued by controversy over the Government's consistent failure to increase capacity, will contact tracing really be ready for a surge of cases in the coming months? Marc Daalder reports
Analysis: The Government is insistent that contact tracing will hold up during any potential summer surge in cases but all the signs currently available point to a system that is already under immense stress.
Nearly a third of close contacts have yet to receive a test, even though they're supposed to get one immediately after being notified. That's in part a symptom of a failure to notify 31 percent of close contacts in the first place - only 69 percent have received a call from contact tracers.
These statistics highlight a system straining at the seams to manage the current caseload. The Government says capacity is being increased, but is unable to say how many contacts a day the system has the ability to trace right now.
Optimistic assumptions
That's a change from the recent past. On October 6, a spokesperson for the Ministry of Health said the system could handle 1000 new daily cases or 6000 new contacts each day.
Right now, we have just under 6500 contacts in total for the past 14 days and tracers are still struggling to keep up.
Director of Public Health Caroline McElnay later let slip what appears to be a more accurate figure. "I think the latest that I heard yesterday was about 170 to 180 cases a day would start to really put pressure on the system as a whole," she said on October 14.
The Government then began to make changes to contact tracing. At the start of the outbreak, officials had widened the definition of a close contact to include people who might previously have been classified as casual contacts. This saw the number of contacts balloon to over 40,000 at one point.
Officials have now narrowed the definition based on the fact that relatively few of these contacts ended up testing positive. Now, many people who would previously have been categorised as close contacts are also allowed to go to work and school with no testing or isolation requirements unless they develop symptoms. Public health officials are no longer attempting to find the origins of every case.
Looking back, the Ministry of Health now says McElnay's mid-October estimate was overly optimistic.
The system was originally only designed to handle 180 to 270 daily cases during national lockdowns, a spokesperson told Newsroom. That's well short of the 1000 daily cases the ministry was instructed to be able to handle as far back as April 2020. But even that lower threshold was missed in October.
The Government's faith that it will be able to handle the coming caseload is based on heroically optimistic assumptions.
"The very high levels of complexity of cases seen during October impacted the estimations for the number of cases that could be managed per day given the emphasis on following up even casual contacts at that stage in the outbreak. Taking that approach, at that time, meant that it was estimated that public health units had capacity to manage between 100-120 cases per day with the ability to surge up to 150 cases per day for limited periods of time," the spokesperson said.
At that stage, the system was failing to manage just 2322 contacts.
Current capacity unknown
So what is the current capacity of the system?
The Government is unable to say. When asked two weeks ago, a Ministry of Health spokesperson said the system was coping with the then-current caseload of 154 cases per day. Efforts were underway to increase capacity by a further 150 cases per day.
As of Monday, the seven-day average case count was 186 daily cases.
The total number of contacts is now 6473 and there are nearly two thousand who have yet to return a test result of any kind. Since publication, a Ministry of Health spokesperson has clarified that just 2.5 percent of contacts are overdue for a test.
Last week, Dr Ashley Bloomfield told Newsroom he was confident that contact tracing would hold up over the summer, even as cases are expected to spread to most of the rest of the country.
"I’m confident in our contact tracing capacity, acknowledging again that the way we’re using it has shifted to be very much focused on those very close and close contacts."
When asked in a written parliamentary question by National MP Chris Bishop whether the contact tracing system was being overwhelmed, Covid-19 Response Minister Chris Hipkins hedged his answer.
"Contact tracing capacity depends on the complexity of cases, and at this stage in the outbreak complexity of cases is high," he replied. "Currently all public health units across the country have stopped non-essential business-as-usual and are completing case investigation to meet high case numbers."
Contact tracing crucial
So the system continues to struggle, with officials and ministers saying that difficulties in October were due to the "high complexity of cases" and that the present challenges have the same cause.
As with past statements of confidence in the contact tracing system, the Government's faith that it will be able to handle the coming caseload is based on heroically optimistic assumptions.
The projections from August through October that the system could handle 1000 cases a day were based on each case having just six contacts – less than a quarter of the reality. The October estimate of capacity for nearly 200 daily cases was based on most cases being simple to trace, not complex. Bloomfield's promises for summer seem to be similarly rooted in an expectation that the complexity of cases will diminish.
There is, however, no reason whatsoever to believe that. In fact, with cases likely to pop up in far more places, each spawning a little outbreak that will be most likely to root itself in the unvaccinated and disengaged, the complexity of contact tracing could in fact increase over the coming months.
Time and time again, the Government has made promises it can't keep on contact tracing. Back in May 2020, then-Health Minister David Clark said that the Ministry of Health's centralised tracing centre could handle 10,000 contact calls per day. Now, the system is struggling with far fewer contacts to manage.
This is a crucial issue because contact tracing could play a major role in reining in the spread of Covid-19. Associate Minister of Health Ayesha Verrall said that contact tracing was expected to provide a 10 percent benefit in reducing transmission under the traffic light system.
Modelling from Te Pūnaha Matatini based on continued Level 3 restrictions in Auckland found contact tracing could play an even greater role. Researchers simulated two worst case scenarios – one with very high rates of transmission and where contact tracing capacity was capped at 1000 cases per day, and another with very high rates of transmission where tracing capacity scaled infinitely with case numbers.
In the former scenario, 6629 weekly cases were expected by the end of the year. In the latter, that fell to just 2332. So case numbers could be up to three times higher if contact tracing slows or stops at 1000 daily cases – and of course the current capacity is well below that 1000 cases per day threshold.
Getting contact tracing right will be key to containing Covid-19 in the coming months but the Government seems to be sleepwalking down the same overconfident path it has taken in the past.
This article has been updated after a response from the Ministry of Health.
