In the UK immunisation programme, the first dose of MMR should be given between 12 and 13 months of age (i.e. within a month of the first birthday). Although immunisation before one year of age provides earlier protection in localities where the risk of measles is higher, but residual maternal antibodies may reduce the response rate to the vaccine. The findings of this study (although associated with a number of limitations due to its retrospective nature) therefore support current practice.