Scientists are waiting for a sample from the Air New Zealand crew member who tested positive for Covid-19 after a flight to China.
The crew member tested negative before leaving on the trip, but tested positive once the plane had arrived in Shanghai.
Air New Zealand said the plane's crew travelled back from Shanghai on a cargo only flight and arrived back in New Zealand yesterday.
While in China, the crew stayed in separate rooms in a quarantine facility managed by local authorities. Several crew members were identified as close contacts of the possible case.
Air New Zealand said they were separated from the person, and other crew members on the journey home.
Dr Jemma Geoghegan, a virologist at Otago University, said she and other researchers are eager to get a sample of the crew member who tested positive to help identify the strain of virus involved.
She said it is difficult to know how someone got the virus when there is no known contact with anyone who had the infection.
"So the only way we can determine perhaps where and when this person became infected is to look at the genome sequence and to compare it to the genome sequences that we have already for the cases that we've had in New Zealand."
But Geoghegan said that will not necessarily provide answers.
It is very likely given that this person is a cabin crew member that the infection could have been contracted in a different part of the world, she said.
"If it is a global case, some international case that this person got infected from then the genome sequence might not exist, so there are challenges."
It is also possible it is an historic infection which may mean there is not enough virus present to be able to sequence a genome, she said.
Despite the fact that it is not yet clear where the person contracted Covid-19, the Ministry of Health is acting as though it was acquired in New Zealand.
The Ministry of Health said the person was retested on returning to New Zealand and returned another positive result, but it said all of the tests for the person's 11 contacts had returned negative tests.
Auckland Regional Public Health Services has released information on locations the person visited prior to leaving the country.
Geoghegan said it is important to remember that a negative Covid-19 test does not necessarily mean that the person does not have the virus.
"A negative test means that there's not enough virus present in the person to detect at that time.
"We've seen this quite a lot of times before, often people will get pre-departure tests even before they come to New Zealand and then show a positive test during their stay in managed quarantine and isolation."
Geoghegan said some research she undertook in conjunction with ESR and the Ministry of Health showed there is very strong evidence that transmission of Covid-19 can occur on a plane during a flight.
She said they looked at a group of people who arrived in New Zealand on the same flight.
"They didn't know each other and their only contact was during the flight," she said.
During their stay in quarantine they tested positive for coronavirus and the plane's seating plan showed they were all seated within a few rows of each other, she said.
"It was very strong evidence that these cases that were genomically linked was actually the transmission occurred during the flight."
She said most of them had tested negative for Covid-19 a few days before the flight.