Nervous system disorders Not known: afebrile convulsions or seizures, ataxia, dizziness, encephalitis (see below), encephalopathy (see below), febrile convulsion (in children), Guillain-Barre syndrome, headache, measles inclusion body encephalitis (MIBE) (see section 4.3), ocular palsies, optic neuritis, paraesthesia, polyneuritis, polyneuropathy, retrobulbar neuritis, syncope