Professor Philip Hill is an epidemiologist on two government Covid-19 advisory groups.
He told Checkpoint the genomic link to a New South Wales returnee is "a game-changer" for stopping the spread in New Zealand.
"It basically suggests that we have a start date for the outbreak. And instead of the possibility the virus might have been circulating for several weeks or even over a month, like maybe it did last year at this time, it may well have only been circulating in the community for a matter of days," Professor Hill said.
However, there will still be more cases appearing, he said.
The genomic sequence tracing tracked the outbreak back to the NSW returnee in MIQ at the Crowne Plaza Hotel in Auckland. Three other people staying in a room across the hallway from the returnee have now tested positive for Covid-19.
Professor Hill said it is an "infection control failure" that needs to be investigated.
It is unclear how significant the infection failure was, he said, but MIQ facilities have done well to keep the virus out of the community in the last six months as the Delta strain has become predominant.
The unlinked case - the Air New Zealand crew member who contracted the virus - is also an infection control failure, Professor Hill said.
