Kiwis are being urged to check that they are vaccinated for measles following a spike in cases, predominantly in unvaccinated people.

Another 20 New Zealanders have contracted measles in the past week, bringing the total number of confirmed cases this year to 135.

Research by ESR has found almost nine in 10 measles patients weren't vaccinated.

Otago University public health expert, Michael Baker, told Kate Hawkesby many young people think they're vaccinated when they're not.

"There's a problem in that age period from about 15 to about mid-thirties, people in that age group have lower coverage and they really need to check that they have had their vaccine."

He said vaccination is a social responsibility.

"It protects those young children, who suffer very badly from measles [and] who are too young to be vaccinated, and also people with compromised immune systems."