The CDHB said it is working to track down those who need to be immunised.
Local GPs are calling anyone in the target age group of 15 to 30, and the health board is working with Māori and Pasifika health providers to reach the community.
It says it has deployed advertising to promote the catch-up MMR jab.
In February last year, the Government promised $23 million to strengthen New Zealand's immunisation system.
Associate Health Minister Julie Anne Genter said at the time 300,000 young people aged between 15 and 29 were not fully protected and would receive the vaccine for free.