MMRV and febrile convulsions
Published 10 December 2025
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Young children with a high temperature (fever) due to infections such as measles, chickenpox and flu can sometimes have a seizure, also known as a fit. These are called febrile convulsions and can happen with a fever caused by anything.
Febrile convulsions usually last a few minutes. Your child may become stiff, have jerking movements, and not respond to you.
1 in 25 children will have a febrile convulsion by the time they turn 5.
Febrile convulsions are common in children aged between 6 months and 5 years. Usually children make a full recovery and have no long-term side effects.
Febrile convulsions following MMRV vaccination
There is an increased risk of having febrile convulsions following the first dose of the MMRV vaccine. This is slightly higher than the risk following the first dose of MMR vaccine.
However, if your child is unvaccinated and catches measles, they are much more likely to have febrile convulsions than after the vaccine.
Number of extra children in 100,000 who may have a febrile convulsion
After measles infection:
- 2,300
After dose 1 of MMR vaccine:
- 24
After dose 1 of MMRV vaccine:
- 35
If you think your child is having a febrile convulsion take them to a doctor urgently.
More information on febrile convulsions is available from the NHS.