What are the side effects of the MMR vaccine?

Millions of doses of the MMR vaccine have been given worldwide for over 30 years. The vaccine has a very good safety record. The side effects of the MMR vaccine are usually mild. It is important to remember that they are milder than the possible complications of measles, mumps and rubella. Side effects are less common after the second dose.

People can sometimes get a sore arm or thigh, where the injection was given. Some may develop a small lump where the needle was put in, and the area around it might also be slightly hot and red. This is normal and may last some weeks. It does not need any treatment.

The vaccine contains weakened types of live measles, mumps and rubella viruses. Because the viruses are weakened, people who have had the vaccine cannot infect other people. The three different viruses in the vaccine act at different times and may produce the following side effects after the first dose.

Around six to 10 days after the vaccination, as the measles part of the vaccine starts to work, about one in 10 people may develop a fever. Some develop a measles-like rash and a loss of appetite. Symptoms usually last two to three days.
About three weeks after the vaccination, 1 in 50 people may get mumps-like symptoms (fever and swollen glands) after their vaccination as the mumps part of the vaccine starts to work.
Rarely, one in every 1000 young children may have a fit caused by a fever following the vaccination. This fit is also called a febrile convulsion. However, if a young child who has not been vaccinated gets measles, they are five times more likely to have a fit.
Very rarely, about 1 in 10,000 people may get a rash of small bruise-like spots in the six weeks after the vaccination. If this happens get advice from your GP.

Less than one in a million people develop encephalitis (swelling of the brain) after the MMR vaccine, but there is very little evidence that it is actually caused by the vaccine. However, if someone catches measles, the risk of developing encephalitis is over 100 times higher.

Less than one in a million people have a severe reaction soon after vaccination, which causes breathing difficulties and may cause them to collapse. This is called an anaphylactic reaction and it can also happen with other medicines and food. These reactions are extremely rare and doctors and nurses are trained to manage them. People who have an anaphylactic reaction can be successfully treated and usually recover within a few hours.

If you or your child has a fever and feels unwell after the vaccination, you or they can take paracetamol or ibuprofen. Read the instructions on the packet carefully and take the correct dose for your or your child’s age. We don’t recommend taking these medicines beforehand to prevent a fever from developing.

Remember – children under 16 should not take medicines that contain aspirin.

For more information on common and rare side effects see:  

If you are concerned about symptoms, call NHS 111 Wales (external site). Calls to NHS 111 Wales are free from landlines and mobile phones.

You can report suspected side effects of vaccines and medicines through the Yellow Card scheme. You can do this online at mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store. Or, you can call the Yellow Card scheme hotline on 0800 731 6789 (Monday to Friday, 9am to 5pm).