Guests mingling inside isolation hotels remains the greatest risk to New Zealand's Covid-19 efforts, as the world continues to struggle to fight Covid-19, an expert says.
Professor Shaun Hendy of the University of Auckland, who has worked extensively on modeling the impacts of Covid-19 here in New Zealand, told TVNZ1's Breakfast programme that the outlook overseas in the short term is "not good news".
He said while some overseas lockdown and containment measures had been effective, some countries were now seeing, or preparing to see, a second wave of Covid-19 infections.
Dr Hendy said the number of confirmed infections in the US - somewhere close to three million - is very likely an underestimate, with a recent CDC estimate putting the likely number closer to 10 times that amount.
While the US outbreak started in areas where people were more likely to take precautions and to do what they could to prevent the spread, people in southern states were less likely to follow government advice, and the true extent of the pandemic in the US is yet to be realised, Dr Hendy said.
"So we might be looking at something like 25 million Americans who have had the disease - but that's still a small fraction of their population - that's still below 10 per cent," Dr Hendy said.
"So they've got a long way to go until they might reach herd immunity."
Herd immunity, where the number of people who have already had the disease and generated immunity is big enough to contain outbreaks in the population, is usually achieved after 60-70 per cent of people have had it, Dr Hendy said.
However, there's still uncertainty as to whether Covid-19 is a disease which actually generates the antibodies required for immunity.
"We still don't know if, once you've had an infection, whether you develop a sufficiently strong immune response to prevent a second infection, or if so how long that lasts - we don't know that," Dr Hendy said.
"We don't know if that herd immunity strategy is in fact an effective strategy."
In New Zealand, incoming travellers leaving isolation as new - and possibly infected - guests enter remains our greatest risk.
"The big thing is to stop mingling of guests. At the moment, if everybody comes in and sticks to themselves and doesn't pass it on to other people, that's very effective.
"The risk is if you come in, the 14 days might mean that you go through the disease and come out non-infectious, but if you pass it to someone, particularly at the later stage of quarantine, then they can come out and infect other people.
"Someone who's almost done their quarantine - but then picks it up and goes out and passes it to the community."
Dr Hendy said the world is still very much in the grips of the disease, and that it's still very unclear as to how long Covid-19 will go on.
"I think it's still very much up in the air how long we're going to have to live with this disease, and of course that depends on when a vaccine comes along," he said.
"I think even parts of the world like Europe - they were hit badly early on, but then have used lockdowns and other public health measures very effectively - they're still very vulnerable to that second wave.
"The majority of the world is struggling to contain the disease, unfortunately."