"This is quite a large outbreak, and something we're very concerned about, and trying our best to implement public health measures to try to contain," Herman said.
She said Auckland was essentially free of the viral disease even late last year, but the outbreak began after being picked up overseas. Herman said it particularly came from the Pacific Islands - mostly Fiji, and later Tonga - where the mumps vaccine was not available.
She said there have also been "massive" outbreaks in the US and the UK, which has spread easily through universities, she said.
"In terms of where the mumps infection is occurring, it's actually all throughout the world. New Zealand has been immune to it until late last year and early this year. Because we've had a vulnerable population here who have not been fully immunised with the MMR vaccine, it's allowed community spread to be well established.
"We are importing mumps, as well as probably exporting it as well."
Two All Blacks - Rieko Ioane and Jack Goodhue - picked up mumps in Auckland. Goodhue had symptoms before leaving and stayed behind, but Ioane - who didn't have any - travelled to London before being isolated and missing Sunday morning's game against the Barbarians. Ioane might also miss this weekend's game against France in Paris.
All Blacks coach Steven Hansen is confident the disease didn't spread to any more of the squad.
Herman said it was not possible to know if the rates of the disease have peaked.
But she said if people have not received the MMR vaccine, to do so immediately. Other ways to combat the spread include washing hands, covering coughs and cleaning commonly used items.
Herman says for most adults, it's a mild illness. However, a small proportion can develop complications including meningitis or encephalitis. Young children are more at risk of developing harmful outcomes.
