A public health researcher says the government needs to step up Covid-19 testing and introduce electronic surveillance of international arrivals.
Professor Michael Baker, from the University of Otago Wellington, says the testing base needs to be expanded and that he wasn't sure whether moves to electronically track new arrivals into the country were immediate enough.
Dr Baker said initial results of the lockdown were positive, but that improved testing should entail swabbing people with other symptoms, such as loss of smell, or testing all healthcare and shop workers.
He said expanding the case definition and priority groups was something the Health Ministry should roll out, given that the health infrastructure was now in place to do so.
"We don't have all the data laid out in a way that people like myself could look at it and say, 'great news. We are testing all around the country in a range of demographic groups and we're not seeing the virus at all'," he told Morning Report.
"At the moment we have really a great increase in test volume, but we just really don't have the breakdown of where the testing's been done.
"We have all the infrastructure now, we have over 100 specialised testing sites around the country and that's very good. The test volumes are rising. The laboratory scientists are, as you've heard, doing amazing things. So, everything's in place, we just need to get that breakdown analysis."
He said that so the Government could effectively determine when to come out of level-4 lockdown response to the virus, wider testing was essential. Essential workers in highly-exposed situations could now be randomly checked in an attempt to pick up undetected clusters.
If health authorities were not seeing evidence of infection in New Zealand, another idea would be to test sewage to pick up traces of the virus.
"This is pooled specimens from a whole lot of people, maybe a whole town or a city, and you can sample that. This is when you are getting to a stage when you really want to know you've got no more virus circulating. Testing is so sensitive it can pic up traces or R and A from the virus."
He said it was a proven method after a study in 2015 measured the rate that traces of an oral polio vaccine excreted by people was being dissipated in the sewerage system, after a change in vaccines was implemented.
He said extending the lockdown was a major decision for government, but that the situation was looking positive. However, before lockdown could be considered, systems of quarantine at the national borders needed to be very effective and that people coming in could be supervised or electronically tracked.
"That becomes are weakest point in the future. The other thing is, you have to have contact-tracing systems working exceptionally well. We've got the sites but we need electronic systems to ensure that happens really quickly," he said.
Earlier on Morning Report, public health professor Nick Wilson said travellers arriving in New Zealand after lockdown might need to be forced to wear electronic bracelets to monitor their movements.
It is likely new arrivals will have to be quarantined after level four and said using tracking technology - in whatever form - would give authorities a huge advantage, Dr Wilson said.
"Whether it's an ankle bracelet or an app on your phone to show your location is shifting from where you're meant to be, the essence of this is supervised quarantine," Dr Baker said.
"This has to be the most critical infrastructure that has to be put in place. That will be the biggest barrier between us and the rest of the world, once we get rid of the virus in New Zealand."
He said he wasn't sure whether moves to out these systems in place were moving fast enough and that it would be a key question as lockdown continued.