A virus has cut Otago rabbit numbers by an average of 34%, but it is still less effective than some farmers expected.

The Otago Regional Council finished the release of the K5 virus at 30 sites about six months ago.

It was released in Roxburgh-Teviot Valley, Wanaka-Tarras, Cromwell-Queenstown and North Otago.

Regional council environmental monitoring and operations director Scott MacLean said the project was successful in that it had been found in the wild rabbit population.

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The virus was more effective in some parts of Otago, due to immunity levels differing across the region, he said.

The average rate of population decline was about 34%, which was close to the range predicted of "up to a 40% reduction", he said.

"We will continue to monitor ... This programme will continue.

"Now that the virus is established in the wild population, it will continue to spread naturally."

Otago Federated Farmers president Simon Davies said he heard from some farmers the release did not have the hoped for effect.

Former president and Wanaka farmer Phill Hunt said it seemed there was more resistance to the virus among rabbit populations than most farmers expected.

"We are seeing dead rabbits, but we're seeing a lot more live ones as well. It's business as usual."

There were high expectations of the virus, he said.

"We'll have to have large-scale poison operations next winter."

He did not think there was anything the council could have done differently.

"I think that they brought it in with the best intentions. It just doesn't seem to have taken quite as well as we were hoping.

"The way they breed, 34% gets replaced pretty quickly this time of year."