It's not possible to say whether any vaccine, including MMR, is absolutely safe. Some children do get side-effects. However, these are very rare after the first dose and even less likely after the second.
The three viruses in the vaccine act at different times and may produce side-effects as they start to work.
The measles part of the vaccine starts to work six to 10 days after immunisation. Your child may have a fever, develop a measles-like rash and/or go off their food. You can give your child a dose of junior paracetamol if he or she develops a fever. However, if the fever persists, contact your child's GP.
About one in every 1,000 immunised children may have a fit caused by the fever. This is called a febrile convulsion. However, the rate of febrile convulsions caused by measles is much higher