There's a mystery behind how a man managed to test positive for Covid-19 after the end of his 14 days of managed isolation and two negative tests.
Health authorities are looking into all possible sources, including whether it was transmitted within a managed isolation facility or had an unusually long incubation period.
There are two household cases connected to a man who tested positive 21 days after returning to New Zealand from India.
He tested negative for the virus on days three and twelve of his stay in managed isolation, and was allowed to fly home from Christchurch to Auckland.
However, last week after developing symptoms and self-isolating; he tested positive.
Genomic testing shows his infection is not connected to the Auckland cluster.
Physics Professor Shaun Hendy has modelled the spread of the virus.
He speaks to Corin Dann.