Scrutiny is falling on pre-departure safeguards for travellers coming into New Zealand, and an expert says they are letting too many Covid-19 positive cases through.
Since mid January, people arriving in New Zealand from most countries have had to prove they had a negative test before their flight - or risk a fine of up to $1000.
But "fake negative" test certificates are being offered for sale, and Director-General of Health Dr Ashley Bloomfield has directed officials to investigate the pre-departure testing regime.
Customs figures showed the vast majority of the roughly 15,000 people who have arrived since the requirement for the negative test had provided it. But it had also issued 33 warnings - most of them shortly after the rule was introduced.
Ten people who arrived on the same flight with Covid-19 this week all had pre-departure test certificates. And Prime Minister Jacinda Ardern said the 10 cases highlighted the shortcomings of pre-departure tests, which could be done 72 hours before people left.
Epidemiologist Michael Baker told Morning Report that border control is the key way New Zealanders are being protected from the virus, and the gaps needed to be plugged.
"At the moment we clearly have infected people who are getting on flights to New Zealand who should have been picked up by testing in that previous three days, and they're not. So something's going wrong there.
"And these infected people, we know they're infecting other people on the flights. This is a real problem for New Zealand because this is what drives the risk for New Zealand, and we are unfortunately getting regular border breaches..."
He said there were weaknesses in the way travellers' negative-test certification was being managed that could be strengthened easily.
"I think we should be communicating to people that there will be an audit of test results, so they know there'll be scrutiny.
"I've talked to several travellers, and there's a very cursory look at their documentation, often someone at the border will look on their mobile phone - that they've got some documentation there. It's not really a system that's got very much scrutiny at the moment."
A Ministry of Health spokesperson said the quality of testing varied around the world and it was looking into whether some of those cases were historical.
Fake pre-departure certificates were not "regarded as a significant issue," she said, and there was little solid evidence of the benefits of pre-departure testing to keeping numbers low in managed isolation.
"A traveller can return a completely authentic negative test before travelling, but won't catch a diagnosis particularly during the early stages of infection," she said.
But Professor Baker recommended two other measures to improve the value of the pre-departure tests.
"We have to keep remembering this isn't a substitute for MIQ", but "travellers should all change their behaviour for at least a week before they travel [to reduce their risk of catching the virus], and that information should be really clearly communicated to them.
"And the second thing is, they require a negative test result and we could be using our booking system to record a lot more information about that test, so they record what laboratory they're going to use, when they're going to get it and so on."
A managed isolation and quarantine spokesperson said they knew of 40 people who had cancelled their spot in managed isolation because their pre-departure test had been positive.
A New-Zealand based cyber security expert said it was concerningly easy to obtain fake Covid-19 test results and vaccine passports on the Dark Web.
Joerg Buss from Darkscope International told First Up its scanning of Dark Web pages had found fake test results on offer, and it showed there were increasing discussions about test results taking place, including on a New Zealand Dark Web forum.