Infectious disease expert Michael Baker says it is unlikely the woman at the centre of a Covid community case scare in Northland caught the virus while she was in Europe.
She travelled first to Spain, and then onto the Netherlands, where she stayed with family, before flying home from London.
A couple of her relatives have tested positive for the virus since she left.
However, she stayed overnight at an airport hotel in London before her flight out of the UK, and arrived in Auckland on 30 December.
It means the last possible contact she had with her relatives would have been on 28 December.
She started showing symptoms on 15 January, nearly three weeks later.
Even if she caught it on the flight over from the UK, that would still mean the virus lay dormant for more than two weeks.
"That would be a very long incubation period," said Baker, a Professor of Public Health at the University of Otago.
The World Health Organisation says the average incubation period is five to six days, but "can be up to 14 days."
"Just based on the information we have in front of us, the most likely scenario is an infection in the MIQ facility," Professor Baker said.
Thirteen people who were staying in the same isolation facility as the woman tested positive over the two weeks she was there.
According to Director-General of Health Dr Ashley Bloomfield a number of them were infected with the more infectious strains.
"These variants of course are thought to be perhaps 50 percent or even more, infectious.
"It just means that we have to do everything much better and much faster than usual, to avoid the virus getting away, or getting out of control.
"It just makes it that much harder, and increases the risk."
A data modelling expert in the past has said that a community outbreak of one such variant would need a level 4 lockdown to bring it under control.
In this case, the exact strain of the virus is still unknown, but the government is working under the assumption it is one of the more infectious strains.
Given the nature of the woman's movements, Baker has called for a rethink of how people leaving managed isolation are allowed to go out.
"The most important measure would be, I think, to make sure people are home quarantining, or something close to it, for that week," he said.
"I mean, no one should say, after that period, it's just business as usual, because it shouldn't be for people leaving MIQ."
Baker told First Up: "I think everyone's working on the basis now that an increasing proportion of infections that come into New Zealand are the more infectious variant but that will all be revealed I think today based on the genome testing."
He said while MIQ facilities are well run, they are not perfect and with thousands of people now moving through them, it was time to consider "turning down the tap" to reduce the number of new arrivals from countries with high numbers of cases of the new variants.
Baker told Morning Report the virus had changed and the risk levels had gone up "considerably" for two reasons: there were more infected people getting on flights, and there was a higher number of people infected in the source countries - many with the more infectious variant of the virus.
He said there was a need to relook at the management of people addicted to cigarettes or nicotine while in isolation, referring to the infection case at Sudima Hotel in Christchurch.
"Smoking is a real problem for infection control."
As for a change in alert levels, he said there was no need for it until there was a sign of community transmission.
"We've got a good contact tracing system, it sounds like this will be manageable.
"I'm much more concerned about the next six months when the risk for New Zealand is going to rise considerably from this force of infection."
There was a need to look at the situation before people board flights, he said, suggesting quarantine and a rapid test before travel.