[M T]

Isn't it also possible that it was contracted by interaction with asymptomatic residents in NZ?  (And I get that it would have to involve multiple asymptomatic transmitters, but still).

Or has every person in NZ been tested (and continues to get tested)?

100 days without known cases requires an string of asymptomatic cases.  Based on a 4-day period between infections (as I recall has been reported in studies), that's 25 rounds of infection.  Even based on people being both being asymptomatic and a long-term carrier, this would probably would require several rounds of them.

Smuggling is also another way this could happen.
I suppose false negative test results could be considered.

Genome studies may help determine if the new cases are closely linked to months-old cases, or to cases now happening elsewhere.

[M T]

Isn't it also possible that it was contracted by interaction with asymptomatic residents in NZ?  (And I get that it would have to involve multiple asymptomatic transmitters, but still).

Or has every person in NZ been tested (and continues to get tested)?

100 days without known cases requires an string of asymptomatic cases.  Based on a 4-day period between infections (as I recall has been reported in studies), that's 25 rounds of infection.  Even based on people being both being asymptomatic and a long-term carrier, this would probably would require several rounds of them.

Smuggling is also another way this could happen.
I suppose false negative test results could be considered.

Genome studies may help determine if the new cases are closely linked to months-old cases, or to cases now happening elsewhere.