Health authorities say three people have been diagnosed mumps in Tauranga this month.
However, there were concerns more people might unwittingly be carrying, and passing, on the virus.
Toi Te Ora Public Health Organisation chief medical officer Neil de Wet said mumps could have serious health complications including swelling of the brain, loss of hearing, and potential infertility in young men but these were rare.
Dr de Wet said there had been an increase in mumps cases in New Zealand in the past year but most of these were in Auckland. Up until last week, there had been three confirmed cases in the Bay of Plenty District Health Board area.
"In the past, our immunisation rates have been very low so people who are now in those two age groups - 10 to 19 and 20 to 29 - historically they had low immunisation rates. It's not surprising that we are seeing most cases in these age groups."