The Ministry of Health has taken a giant step backwards in how long it takes to isolate someone's close contacts from the time they first have Covid-19 symptoms.
It is now taking nine days to isolate 80 per cent of close contacts from the first symptoms of the source of a chain of transmission (the index case).
In the first week of May it was taking only five days - described by director general of health Ashley Bloomfield at the time as "promising" progress.
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The Ministry explained the regress as one or two cases taking a long time and disproportionately impacting the overall data.
Contact-tracing is a key plank in the ongoing pathway to eliminate Covid-19, and while it is less vital in light of seven days of no new cases, it will be crucial if a second wave breaks out.
Contact-tracing will also be a factor in when Cabinet decides no later than on June 22 whether the country is ready to move to alert level 1.
The Ministry has just published its latest data on contact-tracing, which covers April 13 to May 11, a period in which New Zealand was in alert levels 4 and 3.
The data shows that the Ministry is hitting only one of its three targets:
• 71 per cent of people are being tested within 48 hours of their first symptom; target is 80 per cent
• 79 per cent of test results are returned within 24 hours of a swab; target is 80 per cent
• 83 per cent of close contacts are being isolated within 48 hours of a positive lab result; target is 80 per cent
Maintaining success on the latter target will be harder after the limit on social gatherings was eased to 100 people, which means any positive case could have many more close contacts than in the past weeks.
These numbers are more or less the same as the previous data set from April 13 to April 27, though there is a notable improvement in how quickly test results are being returned.
The latest data covers 141 cases and 351 close contacts, reflecting the nature of the lockdown when most cases' close contacts were merely the two to three people in their household bubble.
The Ministry's information release did not include the end-to-end timeframe of the contact-tracing process - from an index case's first symptoms to isolating 80 per cent of close contacts.
That data was released only after the Herald requested it.
A Ministry spokesperson said in a statement that thsi data is not routinely published because of accuracy issues.
"This is due to the fact that many people can not always remember when they first had symptoms as their symptoms may have been mild. People may also delay getting tested which also affects the metric.
"This emphasises the importance of people who have symptoms seeking advice quickly about getting a test."
The spokesperson said that taking a long time to contact-trace for one or two cases can impact the data, given the small number of cases in the second week of May.
"This is what has happened in the latest data. For example, if one or two people take longer to choose to have a test can have a disproportionate impact on the metrics.
"Another example is that in one instance a person initially tested negative, but tested positive as part of cluster surveillance testing."
Contact-tracing has been a success story, given that capacity was abysmal in mid-March when the system could trace only 10 actives cases at a time when there were already 125 cases in New Zealand.
Urgent work was done to ramp up capacity, and Bloomfield has described the current system as "gold standard".
Capacity is still being ramped up to be able to contact-trace 500 cases a day by the end of June.