Health NZ is unable to tell if spending millions to ramp up the health system to cope in winter has actually worked.
The $42 million plan, enacted in 2023, aimed to boost eight areas, such as immunisation and acute treatment flow.
But a newly released document concluded "few conclusions could be drawn" about the success of the plan.
Health Minister Dr Shane Reti had asked what the initiatives cost and if they worked.
But a March report found the evaluation was not clear enough, looked at too few outcomes and had incomplete or inconsistent data on which to rely.
"Overall, the evaluation was unable to provide conclusive evidence that the plan had a direct impact on system pressures, nor was it able to say that the plan had no impact," Reti was told.
"Little was able to be drawn about the cost-effectiveness of the initiatives in the plan."
The eight areas were split into 24 initiatives, which the report said were too many to keep track of.
"The inclusion of a large number of initiatives meant determining any change due to the plan is difficult."
However, it appeared there was more use of telehealth, pharmacies and GPs for minor ailments, the report said.
Half of the money went into trying to strengthen "primary options for acute care". The funding, taken from Te Whatu Ora's baseline, was still being spent after winter 2023 ended, up until mid-2024.
The plan was meant to specifically improve Māori health, but did not. It was mostly not co-designed with Māori, and there was largely "no evidence of greater impact of the plan for Māori", the document said.
Future plans for winter should take a narrower focus - for example, on telehealth, or the flow of elderly patients in a hospital, it concluded.
Planning for winter 2024 was not evaluated in the document.