Closing the door to New Zealand residents - but not citizens - from Covid-ravaged countries will do a lot to keep our border controls from collapsing under a massive influx of cases.
The move has quelled fears that the 1300-odd fortnightly rooms freed up by the transtasman bubble would be taken by arrivals from places like India, where new daily case numbers continue to skyrocket.
In the eight weeks to April 11 - when the temporary travel ban on India came into effect - there were 1797 arrivals from the four countries designated as "very high risk": India, Pakistan, Brazil and Papua New Guinea.
The proportion of arrivals who tested positive over that period - according to Te Pūnaha Matatini principal investigator Professor Michael Plank - was 8.6 per cent for India, 7.8 per cent for Pakistan, 7.3 per cent from Brazil and 6 per cent from PNG.
But the potential for cases bulging at the border was much higher because the proportion of cases from India jumped to between 10 and 15 per cent of arrivals in the most recent weeks.
And it may have soared to 30 to 45 per cent if the temporary travel ban had not been put in place, given the number of new daily cases there has roughly tripled in the past fortnight.
With an average of about 190 weekly arrivals from India, that would have translated to between 57 to 86 cases in our MIQ facilities a week.
Instead, Covid-19 Response Minister Chris Hipkins has narrowed the door as much as possible without breaching the rights of citizens abroad to come home.
When the new restrictions for very high risk countries come into effect from April 28, we will see 43 to 64 fewer cases a week than we otherwise would have - based on his estimate passenger traffic will slash by 75 per cent.
These estimates may play out differently in the real world, given the number of other variables such as people's inclination to travel and future Covid trends.
But it's clear the risk-based measures - the likes of which public health experts have been calling for for months - will have a significant impact.
We may still get more cases in MIQ than we're used to by leaving the borders open to citizens and their families in those countries, especially if the daily case numbers there continue to swell.
But the chances of that have been minimised by the United Arab Emirates barring entry of travellers from India for 10 days from April 25; most travellers to New Zealand from India come via the UAE.
The risk of infected arrivals from the other countries will be countered by the new cohorting measures to keep passengers on the same flight together for their MIQ stay, which should reduce the chances of returnees leaving MIQ with the virus.
The cohorting will also reduce overall risk simply because the number of passenger arrivals by flight will not perfectly match the number of available rooms in one MIQ hotel.
This is expected to lead to between 400 to 600 additional empty rooms, which, in addition to the 500 empty rooms for transtasman bubble contingencies, will mean total MIQ capacity will fall from 4500 rooms pre-bubble to about 3500 rooms.
Most of the 1300 rooms a fortnight freed up by the transtasman bubble, then, will be left empty.
Keeping the rest - a few hundred a fortnight - for arrivals with as much risk of having Covid as people travelling from Australia (practically zero risk) will mean the overall risk profile at the border remains the same.
Hipkins has signalled more low-risk arrivals - seasonal workers from the Pacific and foreign students from countries with no community transmission - for some of those rooms. Reuniting split migrant families will also take some.
Others are likely to be used by returnees from countries with more Covid than Australia, and if so, stronger border measures would offset any additional risk.
Daily saliva tests for MIQ workers would help. As would a full audit of employers at the border to see whether workers are being properly tested.
For now, Hipkins has managed to keep the risks at the border from soaring in parallel with what continues to be a growing global pandemic.
The only question mark is whether the threshold - 15 arrivals per month and 5 per cent of them testing positive - for a "very high risk" country is too low.
The lion's share of arrivals from those four countries - 85 per cent - are from India.
Only 17 people a week arrive from Brazil and PNG, which translates to one extra weekly case that would otherwise not have arrived.
Add Pakistan and the number of extra weekly cases doubles to two.
It leaves an impression that the Government kept the arrivals-per-month test very low to make it look like it wasn't singling out India.