Before the autism-related controversy started in 1998, some concern had already arisen about the safety of the MMR vaccine due to side effects associated with the Urabe mumps strain, including rare adverse events of aseptic meningitis, a transient mild form of viral meningitis.[26][27] A late-1980s trial in Britain of a form of the MMR vaccine containing the Urabe mumps strain produced three cases of probably associated febrile convulsions per 1,000 vaccinations. Concerns about adverse reactions to the vaccine were raised by American and Canadian authorities based on reports from Japan linking Urabe MMR with meningoencephalitis. Canadian authorities withdrew a Urabe-based vaccine in the late 1980s.[28]