Chris Hipkins says if the COVID-19 vaccine rollout drags into next year, Kiwis who don't book vaccinations - or fail to show up when they do - will be to blame.
The COVID-19 Response Minister told The AM Show on Wednesday he welcomed Tuesday's report from Auditor-General John Ryan, which said there was "a real risk that it will take more time than currently anticipated" to complete.
"I think the Auditor-General has engaged in a new type of approach to audits - which is to audit something before it's happened, rather than after it's happened," Hipkins said.
"They've highlighted areas where they think there is risk. I think that is a really constructive approach - it means that those risks can be mitigated and addressed."
Some of the risks noted in the report he said had already been fixed, and others are being worked on.
"It is a big, big campaign. It's going to be one of the biggest things we've asked our health system to do in the short space of time they're going to have to do it, so it is going to stretch things."
Hipkins says the biggest hurdle remains getting the vaccines into the country.
"When we made the decision back in January to say instead of using four different vaccines - which was the original plan - to switch to using the Pfizer vaccine only, because it's the one that we think is the best vaccine available to us at this point - that did create a bit of a challenge for us.
"Pfizer said, 'We can supply you with all the vaccines you need, but the bulk of those are going to arrive between July and September - rather than in the first part of the year.' That slowed us down...
'We knew when we made that decision in January not to use AstraZeneca, not to use the Janssen vaccine yet, not to rely on Novavax - which at the moment hasn't got to the point where it would be ready for approval anyway - when we made that decision we knew that would have some implications for how fast we could move, but I still think it was the right thing to do."
The AstraZeneca and Janssen (Johnson & Johnson) vaccines - both of which use viral vector technology - have had rocky rollouts, being linked to rare cases of blood clots. Some countries have even stopped using them, despite experts saying the adverse effects are incredibly rare.
The Pfizer vaccine, developed with German company BioNTech, uses a newer technology called mRNA. Neither it nor Moderna's similar offering have been linked to anything quite so serious. Novavax says it's unlikely to get authorisation in the US for its protein-based vaccine until July, and won't be able to ramp up production until near the end of the year.
Asked if he could have done one thing differently, Hipkins said it would have been to order enough of the Pfizer vaccine for everybody from the start.
"In the end, we ordered a balanced portfolio - four different vaccines and different quantities of each of those. We didn't know which were going to be most effective. Had we made the decision back late last year, middle of last year when we were ordering, and ordered 5 million courses of Pfizer and not ordered one of the others, and one of the others had proved to be the most effective, then I'd be sitting here saying I'd regretted that.
"So ultimately, we didn't have a crystal ball back then. We made sure that we were hedging our bets, if you like, around what we purchased. Pfizer's proved to be the most reliable, the one we've got the most confidence in, and so we increased our order for it. Had we known that earlier, we might have been able to get it earlier. But that's just all hypothetical, really."
So far the vaccine rollout has focused on border workers and the most vulnerable - the rest of us will get ours in the wider rollout once the jabs have arrived. Hipkins says he still expects the initial rollout - not including any potential booster shots - to be completed this year.
"If New Zealanders come forward and get their vaccinations and we don't have to chase people, they come forward when they've got their appointments, they show up to the appointments that they book and we don't end up with a system that's disrupted by people not showing up and all of those kinds of things, then yes we can.
"If we find that people aren't coming forward and we have to go out and chase people, that's one of the things that will slow this down. Every one of us in the team of 5 million has a role to make sure this is successful. That means when you make an appointment, show up to your appointment. When you book in for the follow-up vaccine three weeks later, make sure you show up for that one too.
"If everybody does that, then we're more likely to get through it by the end of the year. If people don't, that's the sort of thing that will push us into next year."
A survey by AUT communications researchers released this week found about one-in-10 Kiwis aren't planning to get vaccinated at all, and a similar number are unsure, but leaning towards no.
Groups opposed to the vaccine rollout have ramped up efforts in recent months, distributing flyers of misinformation and even challenging it in court.
"Even after a year of testing vaccine efficacy and Government approval, we're still finding a quarter of Kiwis a bit hesitant or sceptical about the vaccine," Jagadish Thaker, a senior lecturer at Massey's School of Communication, told Newshub. "I think there's still some work that needs to be done in order to reach these [people]."
