The Ministry of Health says the person had recovered and was no longer infectious when they were released.
Via an unscheduled 4.20pm media briefing from Director-General of Health Dr Ashley Bloomfield, the ministry announced on December 16 the country's first case of Omicron had been detected at the Christchurch MIQ hotel.
It turns out that one had already been in an Auckland MIQ for nine days.
The case arrived on December 7 from London via Singapore.
They tested positive for Covid on day 0/1 and the positive result was reported on December 9 in the 1pm written briefing.
On December 9, the day the person's positive test was reported by the ministry, there had cumulatively been 568 cases of Omicron reported in the UK, and likely many more unreported.
However, the ministry did not know at the time that the person's travel had originated in the United Kingdom.
The reporting of the case, two days after arrival, said: "Full travel history to be confirmed".
They did report the person had come through Singapore but did not know the origin.
It appears the ministry did not get the positive test result genomically sequenced - which would have told them it was Omicron - until some time later.
"The case was tested before the acceleration of Whole Genome Testing in response to the risk posed by Omicron," a Ministry of Health spokesperson said.
Omicron had already been declared a Variant of Concern by the World Health Organisation 13 days earlier.
It was not until the 1pm update on 19 December that the Ministry reported this person had the Omicron variant, after a number of others had already been reported. The person was already out of MIQ.
This meant the ministry had to track down the rest of the person's arrival flight - 30 other passengers - who they decided should be considered close contacts. This was 12 days after they had arrived. If they were subject to the standard MIQ times, they would have also completed their seven days of managed isolation, three days of self-isolation, and also out in the community, subject to having returned four negative tests (day 0/1, day 3, day 5/6, and day 9 from home).
"As with all border cases," a ministry spokesperson said, "this case was closely managed in MIQ with the appropriate infection prevention controls and PPE.
"This person was able to leave MIQ when they were deemed recovered and therefore no longer infectious."
"All passengers tested negative for the virus, bar one who had a historical infection, which was not the result of in-flight transmission."
