Using a rapid antigen test (Rat) before ending self-isolation could be useful to avoid further transmission of Covid-19, some experts say.
At the traffic light Orange setting, you must self-isolate for seven days if you test positive.
But evidence published in the New England Journal of Medicine shows some cases can remain infectious after seven days.
Covid-19 Modelling Aotearoa co-lead Dr Emily Harvey said it varied from case to case.
"Broadly speaking, international evidence suggests that 10-25% of confirmed cases will still be infectious on day 8 (as measured by live virus that can be cultured in lab)."
"Obviously, this depends a lot on what gets counted as ‘day 0’."
She said because some people would still be infectious at the end of their isolation period, requiring a negative Rat result before being "released" from isolation could reduce onward infections.
A test-to-release scheme could potentially shorten the average isolation period.
"Some people will stop being infectious before day 7.
"Using test-to-release could allow some people to end their isolation early, and shorten the average isolation period, without increasing the risk of onward transmission," she said.
A Ministry of Health spokesman said the ministry acknowledged a small number of people would remain infectious for more than seven days after a positive Rat result.
"A positive Rat is a strong indicator of infectiousness, particularly at the beginning of the infectious period, but as time progresses and an individual recovers, a positive test is less likely to indicate infectiousness."
Eventually, a positive Rat was most likely to represent a false positive result.
Various combinations of testing and a mandatory period of isolation could be considered, but increasing the complexity of a strategy would usually result in poorer performance in practice.
"This is why the ministry does not recommend a Rat at day 7 and why it advises that anyone who has tested positive for Covid-19 should remain at home not only till day 7 after their positive Rat result (or from the onset of their symptoms, whichever is earlier), but also until 24 hours after their symptoms resolve."
