Coronavirus: Returnees could be subject to post-managed isolation COVID-19 test

Returnees to New Zealand who spend two weeks in managed isolation could soon be subject to another COVID-19 test.

At the moment, returnees are tested on day three and day 12 of their stay. But Prime Minister Jacinda Ardern said people could be tested after they've been released from quarantine. 

"This would be an extra precautionary measure to try and reduce down to zero some of that risk," Ardern said on Monday.

It comes as health officials scratch their heads over a positive case from the weekend. A man returned from India on August 27 and isolated in Christchurch for two weeks, but he developed symptoms five days after returning to Auckland and tested positive.

It's not known where he was infected with COVID-19. It could have been in India, on the flight from India or the connecting flight from Fiji. Other people from that same flight also tested positive. There's also a chance he caught the virus in isolation or on the charter flight back to Auckland.

So far, 50,000 returnees have spent two weeks at managed isolation facilities across the country.

University of Auckland's professor Shaun Hendy said it's possible the infected man may have carried the virus for more than 14 days without testing positive. He pointed to new research which shows 1 percent of cases could incubate for 20 days.

"We are seeing more cases coming back positive now and so it is a risk we want to manage, and we can do that partly by testing people after leaving managed isolation," he said.

Another way of reducing risk is reconsidering New Zealand's border controls.

In some countries, COVID-19 is still exploding. Epidemiologist and Otago University professor Michael Baker said the country needs to remain on high alert.

"If we find some countries have such intense transmission that we're seeing a lot of imported cases from there, we might want to think hard about that and how we managed that risk," Baker said.

That could mean banning flights from high risk countries, but Ardern said that isn't on her radar.

No new COVID-19 cases were announced on Monday, and none have been linked to the Auckland cluster for seven days now.