A baby is among six Victorians who have contracted measles after being infected by a traveller visiting from Vietnam.

It is the largest cluster of measles in the state since March last year, with the newly infected patients taking the total number of measles cases in Victoria to 22 so far this year.

The infant, who is less than 12 months old, is not seriously unwell.

Another 27 babies and toddlers were potentially exposed at the childcare centre the infected baby attends and were taken to Monash Medical Centre on Wednesday to be immunised with immunoglobulin in a bid to stop them developing the disease.