Dooms,
Below is from The Encephalitis Society:
Measles, mumps and rubella (MMR) vaccine is a very effective way to prevent against these diseases. All three of these infections are important causes of encephalitis, and before MMR vaccine was introduced all three infections were common in the UK.
The vaccine is unequivocally safer than letting children catch the diseases. In a study carried out in Finland between 1982 and 1986 of over half of million children, it was found that the incidence of encephalitis in the three months following a MMR vaccination was no different to the overall incidence. The example below compares the risk of measles with the risk of MMR vaccine.
Measles
1-3 in 1,000 children contracting measles will develop encephalitis concurrent with the measles infection. 10–15% of those children will die and a further 25% will be left with permanent neurological damage.
1 in 1,000 children with measles will develop post-infectious encephalitis.
1 in 25,000 of children (1 in 5,500 children if they are under 1) with measles will develop subacute sclerosing panencephalitis (SSPE) which has a fatal (death) outcome.
1-2 in 1.000.000 children who had vaccination will develop encephalitis from the vaccination which is less than the incidence of all types of encephalitis.