Officials are still on high alert for new measles cases, despite four days with no new infections

The tally still stands at 17 confirmed cases - all no longer infectious.

But sixteen of the more than three-thousand close contacts identified are symptomatic.

National Public Health Service Director Nick Chamberlain says the risk of undetected community transmission is still considered very high.

He says there was a link between many of these cases and Northland, and there was quite a period in between.

Chamberlain says because of the long incubation period, they have to wait some time before they're confident the outbreak is over.