"There is a real risk that it will take more time than currently anticipated to get there."
Ryan noted that problems were inevitable in a programme of this scale and complexity.
"The Ministry has a high-level plan in place, but there is still a lot of work to do. Some aspects of the plan are still not fully developed. Information systems are still being worked on. If everything goes to plan these will be ready, but only just in time."
The audit also found that while New Zealand had secured enough doses to vaccinate all New Zealanders and a number of Pacific countries, uncertainty about when the doses would arrive could affect the timing of the rollout.
Ryan noted there were "significant risks" around the number of vaccinators, the distribution model to ensure doses were delivered to the right place and at the right time, and ensuring that Maori, Pasifika, people with disabilities, and hard-to-reach communities were vaccinated.
"More work is needed to ensure contingency plans are in place in case of any disruption – such as with the vaccine supply, not having enough vaccinators, or a further community outbreak."
The report made six recommendations to help the Ministry of Health improve its communications with the public, complete its contingency plans if there aren't enough vaccines or vaccinators, provide more guidance and clarity to the wider health sector, and being more transparent about the risks around the vaccine supply.
It comes as a vaccination centre in Ōtara site says it may have to cut the number of days it operates unless it urgently gets more vaccinators.
GPs and pharmacies have also been critical of information about their role in the rollout; last week director-general of health Ashley Bloomfield said a third of GPs and a quarter of pharmacies will be involved when the rollout out ramps up.
Concern over communication with healthcare providers was one aspect the report highlighted.
"The Ministry of Health will be redoubling their efforts to make sure those communication channels are open," Covid-19 Response Minister Chris Hipkins said.
He was confident but nervous about the rollout, he said.
"We've always known that this was a really big task, and I am confident we can do it - but it is going to stretch the system.
"We are going to be pulling out all the stops to make sure that everybody can have a vaccine by the end of the year."
If it isn't done by then, Hipkins said the rollout would simply continue until it was done.
"And of course, we might have to do it again next year with a new vaccine anyway."
He highlight the aspect of the report about Māori and Pasifika being less likely to come forward to get vaccinated.
"So when we get towards the end of the year, if there is a lag, it's more likely to affect those communities - that's something the ministry has already been acutely aware of."
Contingencies were already in place to use other vaccines if the larger Pfizer vaccine supplies didn't arrive as expected in the second half of the year, he said.
The Government has purchase agreements with three other vaccines, though are yet to be Medsafe approved.
Training for 5000 vaccinators had also been completed, Hipkins said.
"We'll need to have more than the 5000. But the 5000 gives us a good base to start from, and I expect those numbers will continue to build."
Bloomfield said many of the actions the Auditor-General had recommended were already underway, given the report was done at an early stage of the programme.
"In all areas identified as needing to be strengthened, the programme has made a number of initial changes and improvements. This was done at the time the report was being undertaken, or ahead of it being finalised. Some recommendations have been fully implemented or are largely complete," Bloomfield said.
He said that included providing more detailed rollout data, working with DHBs on sequencing, and working with health providers on their role in the rollout, as well as a new public information strategy.
Bloomfield said he was confident that by June, the majority of those in group 1 and 2 will have been offered a vaccine, as well as "strong progress" in vaccinating the 1.7 million people in group 3.
That group included those over 65 years old, people with underlying health conditions and prison staff and the prison population.
Bloomfield said contingency planning was underway for the scale-up in July and plans and plans in place to deal with a community outbreak.
