At least 300 cases of mumps have been reported to the Auckland Regional Public Health Service since January.

Low immunisation rates in many parts of Auckland mean a "lost generation" is facing a triple threat of disease, according to health authorities.

There have been 300 notified mumps cases in the region since January, which is higher than all the cases of mumps in the previous 16 years combined.

Auckland Regional Public Health Service is warning that a large number of 10 to 29 year olds are also at risk of measles and rubella.

The service said the "lost generation" of unprotected young people was partly due to the MMR controversy in the late 1990s, something which has been thoroughly discredited.

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Young people needed to be sure they had two doses of the MMR vaccine, medical officer of health Josephine Herman said.

"The implications for young adults are deeply concerning, given the risk of non-immune pregnant women catching rubella. This can result in miscarriage or still birth and babies developing severe birth defects."

Any person who had not received two doses of the MMR vaccine could access this for free and families were being urged to check vaccination records if unsure.

Measles was another serious threat to communities with low vaccination rates, Dr Herman said. "It is likely we'll see further measles outbreaks in schools similar to those in 2011, 2014 and 2016. The measles virus is highly contagious and can lead to serious medical complications as well."

Mumps also poses a risk of miscarriage for women who are in their first three months of pregnancy, and in rare cases can cause male sterility.

A number of adults may also have missed out on the second dose of MMR as the timing was moved from 11 years to 4 years in 2001.

"Mumps is now at large in the community and the only way we can stop this spreading further is to achieve high levels of MMR vaccination in the population," said Herman.