A case of encephalitis in a 14 month old girl occurring 27 days after immunization with MMR vacine is reported from the Department of Child Health, Charing Cross Hospital, London, England. She was admitted with 24 hour history of fever and vomiting and a generalized convulsion and a fever (39°C). Shortly after admission she went into status epilepticus and the seizures continued for a further two hours despite heavy sedation. She required artificial ventilation for four days. She had received mumps, measles and rubella vaccine 27 days before admission. There was a fourfold rise in the S antibody titer to mumps virus by complement fixation. The family history was negative for epilepsy or febrile convulsions. Recovery was slow and when discharged 28 days after admission she had odd behavior and visual impairment. Recovery was complete after four months. 
COMMENT. The authors found one case of mumps meningitis as a post immunization complication in a report from Canada but none in the United States. There were three unpublished reports of mumps meningoencephalitis associated with mumps, measles and rubella vaccine in the United Kingdom. It is suggested that at least 30 days follow-up is needed to exclude a possible neurological complication of the mumps vaccination. The failure to follow patients for a sufficiently long interval after immunizations might explain the lack of neurological complications reported with other vaccines.