Auckland health officials are worried a separate strain of measles not linked to cases from overseas may be starting to spread but stress those who have had two MMR vaccines are still protected.
Auckland Regional Public Health Service says there were no measles cases in 2013 until just before the New Year, since when there have been 17 cases.
Auckland medical officer of health Dr Richard Hoskins says several cases have been traced back to the Philippines, where the infection is not uncommon.
But he says that link has not been established in the two most recent cases, which is causing some concern.
"We won't know whether it's a new strand of measles for some time or whether it's the one that's come mostly from the Philippines that we've been dealing with up to date. It is of concern in that what we don't want is a lot of measles spreading in the community."
Dr Hoskins says health officials are working hard to make sure there isn't another outbreak of measles as happened in 2011 and 2012 when more than 500 people were affected.
He says measles is very infectious, and 80 percent of household members who are not immune will catch it from a family member who has it.
But Dr Hoskins says while the public health service is unsure of the origin of measles in those particular cases, it's still the same disease, and those who have had two MMR vaccines are still protected.