Health authorities have found transmission of Covid-19 in Auckland's Jet Park quarantine facility in July was caused by room doors being opened simultaneously.
Brigadier Rose King, joint head of MIQ, said Tuesday the doors were opened simultaneously for a matter of seconds.
The revelation came after three Covid-19 cases were recorded in the same bubble and room in the facility between July 27 and 29.
King said as a result of this investigation there have been immediate changes at Jet Park.
"This is the first time we have seen something like this occur at the Jet Park Quarantine Facility. As such, we’ve made immediate changes to meal delivery and health check procedures to help prevent future episodes of doors opening at the same time.
"There are low numbers in Jet Park currently so we’ve also been able to separate returnees more widely throughout the facility as much as practicable."
Dr Harriette Carr, the Ministry of Health's Deputy Director of Public Health, said the investigation by the Auckland Regional Public Health Service (ARPHS) concluded there were no bubble breaches.
"But it found that the three cases were genomically linked to a person in the room opposite, and not to the pre-existing case within their bubble of four people.
"They found doors to rooms on opposite sides of the corridor were opened at the same time for about three to five seconds on four occasions between July 19 and 27, when a case in the room opposite would have been considered infectious," she said.
"The proximity in time and location when doors were open, and likely sharing of air that may have occurred, is considered the most likely explanation for this transmission. It was confirmed no other returning travellers would have been exposed and staff were wearing appropriate PPE at the time. We’re confident there was no risk to the public as a result of this.
"What this investigation has highlighted is how easily Covid-19 can be transmitted, even in tightly controlled environments."
All cases had the Delta variant. The linked cases did not arrive from the same country, or share flights and they were staying in different managed isolation facilities prior to transfer to Jet Park.
The situation was immediately investigated and, having viewed CCTV footage of the period in question, it was confirmed that the solo-traveller did not leave their room during their stay.
The investigation concluded that doors to rooms on opposite sides of the corridor were opened at the same time for three to five seconds on four occasions between July 19 and 27 when the solo case would have been considered infectious.
Three of the occasions were due to regular meal deliveries and one was a health check.