Parents of young children living in Jersey are being asked to have them vaccinated against the diseases mumps, measles and rubella.
Jersey's health authority says the vaccine is as safe as others
The island's health authority says it is concerned the number of children who have been given the MMR inoculation is worryingly low.
Jersey's target for vaccination is 95%, but the take-up figure is about 68%.
It is thought the low figures follow concerns that the MMR vaccine may be linked to autism and bowel disease.
But Jersey's Public Health Service said the evidence of any link was weak.
It said the inoculation had been researched more thoroughly than any other and had been shown to be as safe as other programmes.
Parents with children who are approaching their first birthday are being sent a letter explaining how programme works and who they can talk to for advice.