Is the MMR vaccine safe?
BMJ Group Medical Reference
The MMR vaccine can cause side effects, but most are not serious. It's very rare for a child to get a serious problem after having the vaccine. (The MMR vaccine includes vaccines for measles, mumps, and rubella.)
Your child may get a high temperature in the three weeks after having the vaccine. This is quite common. There's a small risk that this could cause a febrile convulsion. A febrile convulsion is a convulsion (fit) that can happen when someone has a high temperature. Your child may lose consciousness for a few seconds and shake, or go rigid. But almost all children recover completely from this.
A big study in the US looked at children who had a febrile convulsion after having the MMR vaccine. None of the children had long-term problems as a result. 
There are other, much rarer, side effects that some children get after having the MMR vaccine.
Aseptic meningitis. This is very rare. It happens to about 2 in 10,000 children who have the vaccine.  They get headaches, fever, and inflammation of the protective tissue covering the brain. It's not as serious as the type of meningitis caused by bacteria. Children usually recover fully from this type of meningitis. It's much less likely to happen if your child is vaccinated with the type of MMR vaccine used in the UK.  
Bruising easily. Doctors call this idiopathic thrombocytopenic purpura (or ITP). This is a blood disorder that means you bruise and bleed easily. It happens to between 25 and 40 children in every million who have the vaccine.   Children can also get this problem if they catch measles or rubella. The risk of getting ITP from the vaccine is much lower than the risk of getting it from measles or rubella.  Children usually recover naturally from this condition.
Arthritis and arthralgia. Some studies show that children can get a mild pain in their joints after having the MMR vaccination. 
Very occasionally, children have a serious allergic reaction to a vaccine. This is called anaphylaxis. It can be life-threatening. Anaphylaxis after having the MMR vaccine is extremely rare.  In the UK in 1994, 1 in 100,000 children had anaphylactic reactions. 
The MMR vaccine has been very well studied to see if it might be linked to lots of different diseases. These include asthma, eczema, bowel disease, diabetes, and other serious conditions. In all of these cases, the researchers found there is no evidence that the MMR vaccine causes these conditions.              
None of the studies we looked at found a link between the MMR vaccine and autism. But we know that because there has been so much publicity about this, lots of people worry about it. To learn about the research, see The MMR vaccine and autism.