A Te Pūnaha Matatini Covid-19 modeller says it's not yet time to stop compulsory MIQ for international arrivals, despite Auckland's growing Delta outbreak.
While a group of Otago University public health experts have set out a case for dropping MIQ stays in step with new controls around Auckland border settings, Te Pūnaha Matatini's Professor Michael Plank said there was still a need to minimise the risk of fresh incursions from overseas.
In a paper released today, but carried out before outbreak began, Te Pūnaha Matatini modellers explored that risk, and what strategies could be used to tackle it.
They included vaccination requirements, combinations of predeparture and post-arrival symptom screening and testing using either rapid antigen tests or PCR tests, and post-arrival self-isolation as well as different vaccination rates in the community.
The researchers found that, if vaccination was required as a condition for travel, reducing the required MIQ stay from 14 days to seven days resulted in a small increase in risk, with around one in 200 infected travellers expected to bring the virus into the community.
By comparison, requiring self-isolation for arrivals meant that around one in 60 infected travellers could bring in Covid-19.
If contact tracing could be used to manage border-related cases, the risk of a significant community outbreak fell to around one in 150 infected travellers.
The research also found that using regular rapid antigen tests could give comparable or better outcomes than using less frequent PCR tests.
Strategies that drew on a combination of PCR and rapid antigen tests – particularly, a type called lateral flow tests that haven't been widely used in New Zealand - at different times could benefit from the advantages of both types of test.
The researchers added that the volume of travellers and the risk profile of the countries from which those travellers are coming were key variables determining the number of infectious individuals arriving at the border.
That was "crucial", they said, because, while the current travel volume was approximately 2500 arrivals to New Zealand per week, this could increase substantially with the relaxation of travel eligibility and quarantine requirements.
For example, a hypothetical scenario with 50,000 arrivals per week – or around half that of pre-pandemic levels - and a prevalence of 0.15 infections per 1000 travellers would mean around 7.5 infected arrivals per week.
Under the more optimistic scenarios with high vaccine coverage and five-day self-isolation and testing requirements, the model estimates the risk of a community outbreak to be in the region of 1 to 2 per cent per infected traveller.
Plank said smarter testing offered options for gradually relaxing border restrictions as New Zealand moved into its next stage of the pandemic, with a traffic light system in place to help manage community transmission amid a population that now had a relatively high vaccination rate.
Earlier this week, Otago experts suggested MIQ requirements should be dropped for most vaccinated international travellers arriving here, given the Covid-19 risk they posed was now typically less than that currently for Aucklanders.
However, they said that needed to come with a set of tight control measures like vaccination, testing - and potentially some home quarantine – for people travelling out of Auckland to other regions.
Plank nonetheless argued it would be premature to scrap MIQ requirements.
"I don't think we're quite there yet. That would add cases, and then increase pressure on our contact tracing system, and then on the Auckland border," he said.
"That's still crucial, and over the next few weeks in particular, in terms of managing this outbreak.
"The thing to remember is that the main determinant of risk at the Auckland border is the number of cases in Auckland itself, rather than the border settings themselves."
This week, Prime Minister Jacinda Ardern said experts were still recommending some checks at the border – such as a period of isolation – and that was why the Government would be trialling home isolation for double-vaccinated people in the first quarter of next year.
But she added that having no measures at the border could cause outbreaks to grow significantly.
"Even with self-isolation, there are some estimates that if you had 20,000 citizens—which is what some estimate will return once the ability to self-isolate opens up," she said.
"You've got 20,000 citizens returning—that even with self-isolation, you'll have up to 20 cases a week being seeded in the community."